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Full text of "Limestone wetland mesocosm for recycling saline wastewater in Coastal Yucatan, Mexico"

LIMESTONE WETLAND MESOCOSM FOR RECYCLING SALINE 
WASTEWATER IN COASTAL YUCATAN, MEXICO 



By 

MARK NELSON 



A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL 

OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT 

OF THE REQUIREMENTS FOR THE DEGREE 

OF DOCTOR OF PHILOSOPHY 



UNIVERSITY OF FLORIDA 
1998 



\ 



Copyright 1998 

On Construction Blueprints pp. 55-64 

(Figures 3-1 to 3-10) 

By 

Mark Nelson 






ACKNOWLEDGMENTS 

I would like to thank my dissertation committee and especially its chair, Howard 
T. Odum, who was an invaluable friend, critic, catalyst and inspiration for my work in 
ecological engineering. I was fortunate to have a committee of gifted teachers and 
scientists whose professional fields spanned the topics covered in the research. Mark 
Brown, my co-chair, gave freely of his knowledge of emergy analysis, wetland ecology 
and restoration. K.R. Reddy is a master of wetland biogeochemistry and generously made 
his laboratory available. Daniel Spangler is a gifted theoretical and field hydrogeologist 
who helped design much of the mangrove research. Clay Montague shared his expertise 
in estuarine dynamics and ecological modeling. I owe a debt to all of them for their 
support, guidance and patience. 

The present study would not have been possible without the generous support of 
the Planetary Coral Reef Foundation, Bonsall, CA and Akumal, Q.R., Mexico. The 
wetland systems have been recipients of the hard work, intelligence and care of Abigail 
Ailing, Gonzalo Arcila, John Allen, Mark van Thillo, Ingrid Datica and Klaus Eiberle, 
who share the vision of coral reef protection and bringing appropriate new technology to 
the tropical world. 

I am indebted to Richard Smith, laboratory manager, and the Water Reclamation 
Facility of the University of Florida for making possible most of the water quality 
analyses. Yu Wang, manager of the Biogeochemistry Laboratory, Soil & Water Sciences, 



conducted the limestone/phosphorus analyses, and Biol. Edgar F. Cabrera contributed his 
extensive knowledge of the plants of the Yucatan. 

The Center for Wetlands supported my work with a research assistantship 
and by providing a stimulating environment of creative staff and students. The Centro 
Ecologico Akumal (CEA) contributed the land for the research wetland units and 
financially assisted in their construction costs. Charles Shaw, staff geologist for CEA, 
greatly assisted by sharing his research on the hydrogeology of the region. 

Finally, I would like to thank my colleagues in the Institute of Ecotechnics 
for allowing me the time to pursue this research, and for all the camaraderie and 
challenge during more than two decades of wonderful ecological work. "Friendship, 
honor, discipline and beauty." 






HI 



TABLE OF CONTENTS 

page 
ACKNOWLEDGMENTS ii 

LIST OF TABLES viii 

LIST OF FIGURES x j v 

ABSTRACT ^j 

CHAPTER 1: INTRODUCTION 1 

Scientific Questions in Ecological Engineering of Wastewater 2 

Wastewater Interface Ecosystems in the Tropics 2 

Wastewater Interactions in Landscapes with Soil 

Substrate of Limestone 3 

Salty Wastewater 4 

Using Small-Scale Mesocosm Tests to Evaluate 

Regional Potentials 4 

Problems of Fitting Water Systems to the Landscape 5 

Unique Characteristics of Tropical Coastal Development 5 

Eutrophication Impacts on Coral Reefs 6 

Issues of Human Health 7 

Previous Studies g 

Study Sites in Yucatan 10 

Regional Study Area: Akumal Coastline 10 

Growth and Development in the Yucatan 13 

Sites of Mesocosm Tests 19 

Receiving Wetland 19 

Concepts 24 

Aggregated Conceptual Model 24 

Diversity vs. Trophic Conditions in the Interface 

Treatment System 26 

Ecological Succession in the Treatment Systems 27 

Major Objectives of the Research 28 

Plan Of Study '.'.'."'..' ."28 

Sampling and Measurement 29 

Outline of the Research Report 30 

CHAPTER 2: METHODS 32 

Treatment Systems 32 



IV 



page 

Ecological Engineering Design 32 

Procedures for Start-Up and Management 34 

Seeding with Biota 34 

Field Measurements 35 

Biodiversity 35 

Frequency 36 

Cover 36 

Importance value 36 

Leaf area index 36 

Leaf holes 37 

Surface organic matter 37 

Solar insolation 37 

Canopy closure 38 

Analytic Measurements 39 

Total nitrogen and total phosphorus 39 

Biochemical oxygen demand (BOD) 40 

Chemical oxygen demand 40 

Total suspended solids 40 

Fecal coliform bacteria 41 

Alkalinity 41 

Salinity 41 

Phosphorus Uptake by Limestone 41 

Initial P content and uptake in wetlands 41 

Calcium/magnesium composition of 

Yucatan limestone 42 

Experiments on phosphorus uptake by limestone 43 

Water Budget of Wetland Systems 44 

Economic Evaluation 44 

Emergy Evaluation 45 

Receiving Wetland 46 

Biodiversity 46 

Mangrove Soils 46 

Hydrogeology 49 

Simulation model of water budgets 49 

Evaluating the Potential of Wastewater System for Coastal Zone 50 

Emergy Evaluation 50 

Transformities 51 

Economic Evaluation 51 

Regional Water Budget 51 

Regional Nutrient Budget 51 

CHAPTER 3: RESULTS 53 

Treatment Mesocosms 53 



page 

Design and Operation of the Wetland Units 53 

Ecological Characteristics 65 

Patterns of biodiversity and dominance 65 

Comparison with natural ecosystems 74 

Dominance 74 

Shannon diversity index 81 

Plant cover 81 

Plant frequency 88 

Importance values 93 

Leaf area index 100 

Leaf holes 100 

Surface organic matter 110 

Solar insolation 112 

Canopy closure 112 

Chemical Characteristics and Uptake 117 

Phosphorus 117 

Nitrogen 123 

Biochemical oxygen demand 128 

Total suspended solids 128 

Alkalinity 137 

Salinity 137 

Reduction in Coliform Bacteria 140 

Phosphorus Uptake by Limestone 140 

Ca/Mg analysis of limestone 140 

Initial and uptake phosphorus levels 146 

Experiments on limestone P uptake 149 

Water Budget 153 

Economic Evaluation 153 

Emergy Evaluation 157 

Receiving Wetland - Groundwater Mangroves 176 

Biodiversity 176 

Mangrove Soils 176 

Nutrients 180 

Hydrogeology of Coastal Zone 189 

Cross section 189 

Groundwater 1 89 

Water quality in mangroves 192 

Total nitrogen 1 92 

Soluble reactive phosphorus 199 

Chemical oxygen demand 199 

Total suspended solids 1 99 

Coliform bacteria 203 

Salinity 203 

Simulation of Water in Treatment Units and Mangroves 206 



VI 



page 

Regional Potential of Wastewater System 219 

Definition of Coastal System 219 

Emergy Evaluation 219 

Economic Evaluation 229 

Water Budget 230 

Nutrient Budget 234 

CHAPTER 4: DISCUSSION 247 

Contribution of Research to Science of Ecological Engineering 247 

Ecological Succession in the Limestone Wetland Units 248 

Comparisons of the Akumal Systems with other Treatment Approaches 250 

Comparisons with Temperate Latitude Interface Systems 254 

Comparison of Emergy Indices of the Akumal Units 256 

Role of Limestone Substrate 260 

Seasonal Changes and Effect of the Dry Season 261 

Treatment of Wastewater Containing Sea Salt 263 

Simulation of Hydrological Extremes 264 

Transpiration of Treatment Systems 264 

Maintaining Vegetative Biodiversity 265 

Impacts of Effluent Disposal on the Mangroves 266 

Carrying Capacity for People - Coastal Development Potential 267 

Percent of Economy Required for Wastewater Processing 268 

Perspectives from Regional Simulation Model 269 

Future Potentials of the Designed Treatment System 276 

Long-Term System Prospects 277 

Authorization Meeting in Mexico 279 

Questions for Research 280 

Biodiversity 280 

Mangrove Change 281 

Useful Life of the Wetland System 281 

Acceptability and Affordability by Local People 281 

Summary 282 

APPENDIX A WATER LEVEL DATA FOR AKUMAL 284 

APPENDIX B NOTES AND TABLES FOR WATER BUDGET 

SIMULATION MODEL 304 

APPENDIX C COMPARISON WITH UNIVERSITY OF FLORIDA 

SEWAGE TREATMENT FACILITY 314 

REFERENCES 319 

BIOGRAPHICAL SKETCH 330 



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TABLES 

page 
Table 2-1 Transformities values used in emergy evaluations in this study 52 

Table 3-1. Plant species in the treatment wetlands from surveys of May 1997, 
December 1997 and July 1998. Total number of species as of May 1997: 
68 species; as of December 1997: 70 species, as of July 1998: 66 species 66 

Table 3-2 Species list: mangrove wetland ecosystem, 8 December 
1 997. Species identified by Edgar Cabrera, Chetumal, Q.R 78 

Table 3-3 Species list of inland forest near Akumal, Q.R., 9 December 
1997. Species identified by Edgar Cabrera, Chetumal, Q.R 79 

Table 3-4 Shannon diversity indices for constructed wetland systems 
based on May 1997, December 1997 and July 1998 surveys 82 

Table 3-5. Comparison of Shannon diversity indices for constructed 
wetlands vs. natural mangrove and tropical forest ecosystems of the 
study area, based on December 1997 and July 1998 survey data 83 

Table 3-6. Relative cover in the wetland system cells, based on 0.25 
sq m quadrant analysis, May 1997 84 

Table 3-7. Estimates of area coverage, including canopy, of dominant plants in 
the wetland treatment cells, May 1997. Total area of each cell in system 1 is 25.3 
square meters, and area of each cell in system 2 is 40.6 square meters 85 

Table 3-8. Estimates of area coverage, including canopy, of dominant 
plants in the wetland treatment cells, December 1997 and July 1998. 
Total area of each cell in system 1 is 25.3 square meters, and area of 
each cell in system 2 is 40.6 square meters 86 

Table 3-9. Frequency rankings of dominant plants in constructed 
wetlands in May 1997, December 1997 and July 1998 transects 89 

Table 3-10. Importance value ranking of top eight species in each wetland treatment 
cell, May 1997, December 1997 and July 1998 surveys. Values were computed by 
adding relative species frequency and relative species cover and dividing by 2. 
Maximum value is therefore 1.0, and total is 1.0 summing all species found 



Vlll 



page 
in the treatment cell 94 

Table 3-1 1 Measurements of leaf area index in the treatment cells of the 
wetland systems, May 1997, December 1997 and July 1998. Values are 
given with standard error of the mean 101 

Table 3-12 Leaf holes in the wetland treatment units, December 1 997 1 06 

Table 3-13 Leaf holes in the wetland treatment units, July 1998 data 108 

Table 3-14. Outside solar insolation levels and their reduction in the 
constructed wetlands, 28 July 1998 between 1050 and 1 145 AM. 
Perimeter light levels are the measured insolation at locations 0.5 m inside 
the wetland systems along their outside edges 113 

Table 3-15. Light penetration and canopy closure in the wetland systems and 
adjoining mangrove wetland, 29 July 1998. Data presented ± standard error 
of the mean 115. 

Table 3-16 Total phosphorus content of water samples from cenote 
(groundwater well) near wetland treatment systems 120 

Table 3-17 Total phosphorus in effluent from septic tank and discharge 
effluent from wetland treatment systems and percent reduction of 
phosphorus levels 121 

Table 3-18. Total phosphorus content of water samples from the 
treatment wetlands 1 22. 

Table 3-19 Total nitrogen in effluent from septic tank and discharge effluent 
from wetland treatment systems and percent reduction of nitrogen levels 126 

Table 3-20 Total nitrogen content of water samples from cenote 
(groundwater well) near wetland treatment systems 127 

Table 3-21 Biochemical oxygen demand (BOD-5) in effluent from septic 
tank and discharge effluent from wetland treatment systems and percent 
reduction 131 

Table 3-22 Biochemical oxygen demand (BOD-5) content of water 
samples from cenote (groundwater well) near wetland treatment systems 132 

Table 3-23 Total suspended solids (TSS) concentrations and reduction in 
septic tank and discharge water from the Akumal wetland treatment systems 133 



IX 



page 
Table 3-24 Total suspended solids (TSS) concentrations in water samples 
from cenote (groundwater well) near wetland treatment systems 134 

Table 3-25 Alkalinity in septic tanks, wetland systems and cenote 138 

Table 3-26 Salinity in septic tanks, wetland systems and cenote 139 

Table 3-27 Coliform bacteria concentrations in effluent from septic tank and 
discharge effluent from wetland treatment systems and percent reduction. Data 
is in units of most probable number of colonies per 1 00 ml (MPN/ 1 00 ml) 1 43 

Table 3-28 Coliform bacteria concentrations in water samples from 
cenote (groundwater well) near wetland treatment systems. Data is in units 
of most probable number of colonies per 100 ml (MPN/100 ml) 144 

Table 3-29 Ca/Mg composition of Yucatan limestone as analyzed by inductive 
coupled plasma spectroscopy 145 

Table 3-30. Inorganic phosphorus content of limestone samples 147 

Table 3-31 Results from experiments on limestone uptake of phosphorus 150 

Table 3-32. Daily water budget of wetland treatment systems, May 1997 1 54 

Table 3-33. Daily water budget of wetland treatment systems, December 1997 155 

Table 3-34 Purchased materials and services used in construction of wetland 
systems, Akumal, Mexico. Costs are expressed in Mexican pesos(1996) and 
converted to U.S. dollars at the rate of 7.8 peso/$, which was the exchange 
rate in 1996 when systems were built 159 

Table 3-35 Purchased materials and services used in construction of package 
plant sewage treatment system, Akumal, Mexico. Costs are expressed in 
Mexican pesos (1996) and converted to U.S. dollars at the rate of 7.8 peso/$, 
which was the exchange rate in 1 996 when systems were built 1 60 

Table 3-36 Emergy analysis of the constructed limestone sewage wetlands 1 62 

Table 3-37 Emergy analysis of the package plant sewage treatment system 171 

Table 3-38 Wet weight/dry weight of soils in mangrove receiving wetland, 
December 1997 177 

Table 3-39 Bulk density of soils in mangrove receiving wetland, December 1997 178 



page 
Table 3-40 Organic matter content of soils in mangrove receiving wetland 
estimated from loss on ignition and mean values of the five soil samples 
from December 1997 179 

Table 3-41 Calcium and magnesium content of mangrove soil ash after combustion 
for organic content. Results determined by inductive coupled plasma spectroscopy... 181 

Table 3-42 Total Kejdahl nitrogen content of soils in mangrove receiving 
wetland on 12 December 1997 before discharge of treated effluent 185 

Table 3-43 Total Kejdahl nitrogen content of soils in mangrove receiving 
wetland before discharge (30 April 1998) and 2 months (3 July 1998), 
3 months (3 August 1998) and 4 months (2 September 1998) after 
discharge of treated effluent began 3 May 1998 186 

Table 3-44 Phosphorus content of soils in mangrove receiving wetland 
on 1 2 December 1997 before discharge of treated effluent 1 87 

Table 3-45 Phosphorus content of soils in mangrove receiving wetland 
before and after discharge began 3 May 1 998 188 

Table 3-46 Total nitrogen in water of mangroves before and after discharge 
of treated wastewater 198 

Table 3-47 Soluble reactive phosphorus (SRP) in water of mangroves 
before and after discharge of treated wastewater 200 

Table 3-48 Chemical oxygen demand (COD) in water of mangrove receiving 
wetland before and after discharge of treated wastewater 20 1 

Table 3-49 Total suspended solids (TSS) in water of mangroves 
before and after discharge of treated wastewater 202 

Table 3-50 Coliform bacteria in water of mangroves in 1998 after 

discharge of treated effluent 204 

Table 3-51. Salinity in mangrove water in December 1997 before 
discharge of sewage effluent 205 

Table 3-52 Salinity in mangroves in 1998. Discharge of treated 
effluent began May 1998 207 

Table 3-53 Computer program in BASIC for simulation model of water 
budget in treatment wetland nit 210 



XI 



p age 
Table 3-54 Spreadsheet for calculation of coefficients in water budget 
simulation model of treatment units and mangroves 212 

Table 3-55 Emergy evaluation table of one square kilometer of developed 
coastline, Akumal, Mexico (see Figure 3-58) 22 1 

Table 3-56 Emergy indices for evaluating one square kilometer of 
developed coastline, Akumal, Mexico 227 

Table 3-57 Water budget of a square kilometer of coastline around 
research site without use of wetland treatment systems 231 

Table 3-58 Comparative additions to groundwater (GW) of nitrogen, 
phosphorus, BOD (organic compounds) and fecal coliform in a 1 -square- 
kilometer area of study site with and without the use of wetland 
treatment systems 235 

Table 3-59 Phosphorus budget of a developed square kilometer of 
coastline, Akumal, Mexico, with no sewage treatment and changes if 
wetland systems are installed 237 

Table 3-60 Nitrogen budget of a developed square kilometer of 
coastline, Akumal, Mexico, with no sewage treatment and changes if 
wetland systems are installed 240 

Table 3-61 Organic compounds (BOD) budget of a developed square 
kilometer of coastline, Akumal, Mexico, with no sewage treatment and 
changes if wetland systems are installed 243 

Table 3-62 Coliform bacteria budget of a developed square kilometer of 
coastline, Akumal, Mexico, with no sewage treatment and changes if 
wetland systems are installed 245 

Table 4-1 Comparison of loading rates and removal efficiency of Akumal 
treatment wetland units with average North American surface and subsurface 
flow wetlands (Kadlec and Knight, 1996) 255 

Table 4-2. Comparison of emergy indices for Akumal treatment units, 
package plant at Akumal and the University of Florida wastewater 
treatment system (compiled from data in Tables 3-36, 3-38 and Appendix) 257 

Table 4-3 Program in BASIC for simulation model of interactions between 
natural environment and human economy along the Yucatan coast 273 



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page 
Table B-l . Average monthly rainfall at Tulum, 20 km south of study site 308 

Table B-2 Measured evaporation at Tulum, 20 km south of study site 
along the Yucatan coast. Actual evapotranspiration is estimated at 900 mm 
for the Yucatan. The last column is a calculation of evapotranspiration 
based on the percentage of yearly evaporation that occurs in each month 309 

Table B-3 Average monthly relative humidity, temperature, and air 
vapor pressure calculated for the given temperature and relative humidity 
for the Yucatan coast 310 

Table B-4 Average wind velocity, measured at Puerto Moreles, Mexico, 
80 km north of study site 311 

Table B-5 Estimates of monthly groundwater flow based on data from 
Back (1985) and average monthly rainfall in the Yucatan 312 

Table B-6 Net primary productivity in mangrove ecosystems 313 

Table C-l. Emergy analysis of the University of Florida sewage 
treatment facility 316 



X1U 



FIGURES 

page 
Figure 1-1 Map of eastern Yucatan Peninsula of Mexico showing coastal 
area of study around Akumal, Quintana Roo, north of Tulum 11 

Figure 1-2 Geological cross-section in study area showing flow and mixing 
of fresh groundwater and seawater (Shaw, in press) 12 

Figure 1-3 Map of study area a) shows collapse zones and areas of ancient 
bays (larger black dots) b) shows areas of groundwater discharge along the 
coast and sampling points. In both diagrams modern reef is indicated by 
light dots offshore (Shaw, in press) 14 

Figure 1-4 Salinity contours in Akumal during a period of no rain. 
Contours are compressed on the highly porous and permeable limestone. 
At the 20% contour, mixing of saltwater and freshwater below ground 
surface makes the gradients steeper (Shaw, 1997) 15 

Figure 1-5 Salinity contours in Akumal area after a heavy rain. Compared 
to Figure 1-4, salinity gradient is displaced inland due to dilution by rain 
and groundwater flow (Shaw, 1997) 16 

Figure 1-6 Map of study area showing groundwater flow in relation to 
porous limestone rock (indicated by crosses) and coliform contours from 
studies conducted in May-August 1997 (Shaw, in press) 17 

Figure 1-7 Aerial photograph of study area, Akumal, Quintana Roo, 
Mexico 20 

Figure 1-8 Study area around Akumal, Mexico showing location of the wetland 
systems at "A", enlarged in Figure 1-9. Contour lines in meters. (Shaw, in press) 21 

Figure 1-9 Enlarged sketch of area "A" in Figure 1-8 showing location of wetland 
treatment areas and mangrove where treated effluent was discharged. 
Points labeled A to E are mangrove sampling stations 22 

Figure 1-10 Systems diagram showing the wetland treatment unit within 
the context of the coastal zone economy and ecology 25 



XIV 



page 
Figure 2-1 Schematic of wetland treatment system showing flow from 
houses to septic tanks to wetlands 33 

Figure 3-1 Construction blueprint: isometric view of the wetland treatment 
system 55 

Figure 3-2 Construction blueprint: isometric view of piping in the wetland 
system 56 

Figure 3-3 Construction blueprint: center section view of the wetland 
system 57 

Figure 3-4 Construction blueprint: side section showing fill materials in 
the wetland system 58 

Figure 3-5 Construction blueprint: control box with dimensions of the 
wetland treatment cells 59 

Figure 3-6 Construction blueprint: treatment cell 1 header detail of the 
wetlands 60 

Figure 3-7 Construction blueprint: treatment cell 2 header detail of the 
wetlands 61 

Figure 3-8 Construction blueprint: schematic showing drainfield detail 
for large wetland systems 62 

Figure 3-9 Construction blueprint: schematic showing drainfield detail for 
small wetland systems 63 

Figure 3-10 Construction blueprint: drainfield cross-section drawing of 
wetland system 64 

Figure 3-1 1 Species-area curves for each of the four wetland treatment 
cells, May 1997 data 70 

Figure 3-12 Species-area curves for each of the four wetland treatment 
cells, December 1997 data 71 

Figure 3-13 Species-area curves for each of the four wetland treatment 
cells, July 1998 data 72 

Figure 3-14 Species-area curves for the 50.6 m 2 wetland unit (system 1) 
and the 81.2 m 2 wetland (system 2), May 1997. Transects counted 482 



XV 



page 
individuals in each system 73 

Figure 3-15 Species-area curves for the 50.6 m 2 Yucatan wetland 

(system 1) and the 81.2 m 2 wetland (system 2), December 1997. Transects 

counted 500 individuals in each system 75 

Figure 3-16 Species-area curves for the 50.6 m 2 Yucatan wetland 
(system 1) and the 81.2 m 2 wetland (system 2), July 1998. Transects 
counted 500 individuals in each system 76 

Figure 3-17 Comparison of species richness between treatment wetlands, 
mangrove wetland and forest ecosystems, December 1997. Transects were 
1000 individuals from each system 77 

Figure 3-18 Comparison of species richness between mangrove, forest and 
each treatment wetland. Transects counted 1000 individuals in mangrove 
and forest, and 500 each in wetland systems 1 and 2 80 

Figure 3-19 Plant species in rank sequence of importance value (IV) in 
the four wetland treatment cells, May 1997 data. Importance value = 
(frequency + cover)/2 97. 

Figure 3-20 Plant species in rank sequence of importance value (IV) in 
the four wetland treatment cells, December 1997 data. Importance 
value = (frequency + cover )/2 98 

Figure 3-21 Plant species in rank sequence of importance value (IV) in 
the four wetland treatment cells, July 1998 data. Importance value = 
(frequency + cover )/2 99 

Figure 3-22 Photograph of wetland systems in Akumal shortly after 
planting, August 1996. System 1 is in foreground and System 2 in 
background, in front of edge of mangrove wetland 102 

Figure 3-23 Photograph of vegetation in wetland system 1 , May 1 997 1 03 

Figure 3-24 Photograph of vegetation in wetland system 1 , December 1 997 1 04 

Figure 3-25 Photograph of vegetation in wetland system 1 , July 1 998 105 

Figure 3-26 Surface organic matter in the wetland treatment cells. Data 
presented are those of initial mulching (August 1996) and surface organic 
matter (July 1 998) after 23 months of operation. Bars are ± standard errors Ill 



XVI 



page 

Figure 3-27 Photograph showing dense canopy cover intercepting solar 
insolation, wetland system 2, July 1998 114 

Figure 3-28. An example of canopy-cover photograph using fish-eye lens, 

July 1998 116 

Figure 3-29 Total phosphorus (TP) analyses of water samples from 
wetland treatment system 1 118 

Figure 3-30 Total phosphorus (TP) analyses of water samples from 
wetland treatment system 2 119 

Figure 3-3 1 Total nitrogen (TN) analyses of water samples from wetland 
treatment system 1 124 

Figure 3-32 Total nitrogen (TN) analyses of water samples from wetland 
treatment system 2 125 

Figure 3-33 Biochemical oxygen demand (BOD 5 ) in wetland system 1 
water samples 1 29 

Figure 3-34 Biochemical oxygen demand (BOD 5 ) in wetland system 2 
water samples 130 

Figure 3-35 Total suspended solids (TSS) in water samples from wetland 
system 1 135 

Figure 3-36 Total suspended solids (TSS) in water samples from wetland 
system 2 136 

Figure 3-37 Fecal coliform bacteria in water samples from wetland 
system 1. Data plotted on log scale, and units are most probable number 
(MPN) of bacterial colonies per 100 ml 141 

Figure 3-38 Fecal coliform in water samples from wetland system 2. 
Data plotted on log scale, and units are most probable number (MPN) of 
bacterial colonies per 100 ml 142 

Figure 3-39 Estimates of monthly flows of phosphorus during first year of 
wetland treatment system operations (1997). Data from both wetland 
systems are combined 148 

Figure 3-40 Graphs with results of experiments on limestone uptake of 
phosphorus ]52 



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page 
Figure 3-41 Diagram of emergy and money flows in wetland treatment 
systems, Akumal, Mexico. Units of diagram are E15 sej/yr 172 

Figure 3-42 Diagram of emergy and money flows in the package plant 
sewage treatment system, Akumal, Mexico. Units of diagram are 
E15 sej/yr 180 

Figure 3-43 Howard T. Odum inspecting root penetration and peat depth 
in mangroves, Akumal, December 1997 182 

Figure 3-44 Thickness of mangrove peat in the receiving wetland around the outfall 
pipe discharging effluent, December 1997. See Figures 1-9 for location of mangrove 
discharge point in Akumal. Mangrove soil samples were collected 1,3, 5 and 10 m 
from discharge point in N,S,E and W directions (Tables 3-43 and 3-45). Water 
samples were collected at lm upstream (A), lm (B) 3m (C) and 6m (D) 
downstream and 15m (E) SE of discharge point (see Figure 1-10) 183 

Figure 3-45 Systems diagram of the mangrove wetland receiving treated 
effluent 190 

Figure 3-46 Potentiometric measurements of groundwater level in 
mangroves, December, 1997. Piezometers were located at A,B, and C. 
Survey transit level was located at point D. Flowlines calculated from 
data are approximately in easterly direction 191 

Figure 3-47 Chart recorder water levels in cenote near wetland systems, 
27-28 May 1997 193 

Figure 3-48 Chart recorder water levels at Yal-ku lagoon, showing tidal 
record, 27-28 May 1997 194 

Figure 3-49 Chart recorder water levels in mangrove receiving wetland, 
9-14 December 1997 195 

Figure 3-50 Chart recorder water levels in cenote near wetland systems, 
10-14 December 1997 196 

Figure 3-51 Chart recorder water levels at Yal-ku lagoon, showing tidal 
record, 10-14 December 1997 197 

Figure 3-52 Systems diagram for simulation model of water budgets of 
treatment unit and receiving wetland showing difference equations 208 



XVHI 



page 
Figure 3-53 Systems diagram showing steady state storages and pathway 
flows for water budget simulation model of treatment units and mangroves 209 

Figure 3-54 Computer simulation of the water budgets of treatment 
units and mangroves 215 

Figure 3-55 Simulation of water budget for wetland treatment unit and 
mangroves with increase of wastewater loading (10 times higher). 
Scale: sunlight 5000 Kcal/m 2 /day, biomass 20 kg/m2, water levels 1.5 m, 
water inflows 1 m/day 216 

Figure 3-56 Simulation of water budget for wetland treatment unit and 
mangroves with loss of groundwater inflow. Scale: sunlight 5000 
Kcal/m 2 /day, biomass 20 kg/m2, water levels 1.5 m, water inflows 
lm/day 217 

Figure 3-57 Simulation of water budget for wetland treatment unit and 
mangroves with hurricane event at year 5. Scale: sunlight 5000 Kcal/m 2 /day, 
biomass 20 kg/m2, water levels 1.5 m, water inflows lm/day 218 

Figure 3-58 Map of Akumal, Mexico showing the 1 -square-kilometer 
coastal study area 220 

Figure 3-59 Systems diagram of the square kilometer coastal economy and 
environment, labeled with emergy flows in El 8 sej/yr from Table 3-57 226 

Figure 3-60 Diagram of emergy and money flows in the 1 -square-kilometer 
coastal area, Akumal, Mexico. Units of diagram are expressed 
inE18sej (solar emergy joules)/yr 228 

Figure 3-6 1 Diagram of water budget of one square kilometer of 
developed coastline, Akumal, Mexico. Figures in parentheses show changes 
in budget if all sewage is treated by constructed limestone wetlands 233 

Figure 3-62 Diagram of phosphorus budget of one square kilometer of 
developed coastline, Akumal, Mexico. Figures in parentheses show changes 
in budget if all sewage is treated by constructed limestone wetlands and 
receiving wetlands 239 

Figure 3-63 Diagram of nitrogen budget of one square kilometer of 
developed coastline, Akumal, Mexico. Figures in parentheses show 
changes in budget if all sewage is treated by constructed limestone 
wetlands and receiving wetlands 242 



XIX 



page 
Figure 3-64 Diagram of organic matter (BOD) budget of one square 
kilometer of developed coastline, Akumal, Mexico. Figures in parentheses 
show changes in budget if all sewage is treated by constructed limestone 
wetlands and receiving wetlands 244 

Figure 3-65 Diagram of coliform bacteria budget of one square kilometer 
of developed coastline, Akumal, Mexico. Figures in parentheses show 
changes in budget if all sewage is treated by constructed limestone 
wetlands and receiving wetlands 246 

Figure 4-1. Diagram showing annual emdollar contributions to the 
constructed wetland system in Akumal, Mexico 258 

Figure 4-2. Systems diagram and difference equations used for simulation 
model of the interactions between the natural environment and the human 
economy along the Yucatan coastline 270 

Figure 4-3. Systems diagram for Yucatan coastal model. Values shown 
are steady-state storages and flows between components 271 

Figure 4-4 Computer simulation of the Yucatan coastal model. The 
legend gives the full scale values of the ordinate for each quantity 272 

Figure 4-5 Simulation runs of the interaction of the environment and human 
economy in the Yucatan, a/ Impact of starting with nitrogen at ten times higher 
value b/ Impact of starting with coral at zero c/ Impact of starting with money 
and assets at 1/10 value 275 

Figure A-l Water level record for cenote near wetland treatment unit, 
27-28 May 1997 285. 

Figure A-2 Water level record for cenote near wetland treatment unit, 
28-29 May 1997 286 

Figure A-3 Water level record for cenote near wetland treatment unit, 
29-30 May 1997 287 

Figure A-4 Water level record for cenote near wetland treatment unit, 
30-31 May 1997 288 

Figure A-5 Water level record of tidal heights at Yal-Ku Lagoon, 27-28 May 1997... 289. 

Figure A-6 Water level record of tidal heights at Yal-Ku Lagoon, 

13-16 December 1997 290 



XX 



page 
Figure A-7 Water level record of tidal heights at Yal-Ku Lagoon, 
16-17 December 1997 291 

Figure A-8 Water level record of tidal heights at Yal-Ku Lagoon, 
17-19 December 1997 292 

Figure A-9 Water level record of tidal heights at Yal-Ku Lagoon, 
19-22 December 1997 293 

Figure A- 10 Water level record for cenote near wetland treatment unit, 
10-14 December 1997 294 

Figure A-l 1 Water level record for cenote near wetland treatment unit, 
14-17 December 1997 295 

Figure A- 12 Water level record for cenote near wetland treatment unit, 
17-20 December 1997 296 

Figure A- 13 Water level record for mangrove near wetland treatment unit, 
9-14 December 1997 297 

Figure A- 14 Water level record for mangrove near wetland treatment unit, 
14-17 December 1997 298 

Figure A- 15 Water level record for mangrove near wetland treatment unit, 
17-20 December 1997 299 

Figure A- 16 Water level record for mangrove near wetland treatment unit, 
18-21 July 1997 300 

Figure A- 17 Water level record for mangrove near wetland treatment unit, 
22-25 July 1997 301 

Figure A-l 8 Water level record for mangrove near wetland treatment unit,. 
25-28 July 1997 302 

Figure A- 19 Water level record of tidal heights at Yal-Ku Lagoon, 
24 July -1 August 1997 303 



XXI 



Abstract of Dissertation Presented to the Graduate School 

of the University of Florida in Partial Fulfillment of the 

Requirements for the Degree of Doctor of Philosophy 

LIMESTONE WETLAND MESOCOSM FOR RECYCLING SALINE 
WASTEWATER IN COASTAL YUCATAN, MEXICO 

By 

Mark Nelson 

December 1998 



Chairman: Howard T. Odum 

Major Department: Environmental Engineering Sciences 

To understand wetland self-organization and to prevent pollution of groundwater 
and coral reef on the calcareous east coast of Yucatan, Mexico, a wetland mesocosm 
system was developed for treatment and recycle of saline, septic-tank wastewater. High 
diversity wetland ecosystems were developed in two concrete-lined chambers, using 
subsurface flow through limestone gravel, arranged in series with discharge to backbeach 
mangroves. 

Evapotranspiration in the wetlands averaged 35% of design influent during 
summer months and 20% during winter months. Tall wetland vegetation developed with 
66 plant species in 131 m 2 . Shannon diversity of vegetation was 5.01 (logarithm base 2), 
far greater than that of the mangrove wetland (1.49), but less than the inland Yucatan 
forest (5.35). Leaf area index increased over 13 months from 3.96 ± 0.28 to 6.05 ± 0.49. 



XXII 



In wastewater passing through the systems, biochemical oxygen demand was reduced 
85%, suspended solids 40%, phosphorus 78% and nitrogen 75%. Coliform bacteria were 
reduced 99.8+%. Limestone gravel in the treatment system removed 5.75 ± 1.68 mg/kg 
phosphorus per year. Nutrients in mangrove water and soil sediments increased 5-10% 
from discharge of treated wastewater. Water budgets in treatment system and mangrove 
were studied with simulation model. 

On a per-capita basis, the wetland systems for 40 people cost approximately $160 
per person to construct, vs. over $400 for alternative treatment technologies. Operation 
and maintenance costs were 10% that of conventional treatment. Emergy in purchased 
inputs for construction were less than 1/3 of free environmental inputs; empower density 
was 2.5 E19 sej/ha/yr (one third that of conventional treatment). 

The potential for economic development using the new treatment systems was 
evaluated. Treatment systems would require 0.3% of the annual monetary flow (vs. 1.1% 
for conventional sewage treatment) and 2.4% of total emergy while contributing 71,000 
emdollars (the monetary equivalent of useful work contributed by nature and by humans). 
The new systems conserve mangroves, reduce eutrophication, prevent pollution of 
groundwater, protect marine resources, and contribute aesthetic values. 

Research results indicate high biodiversity can be achieved in sewage treatment 
wetlands, use of limestone gravel augments phosphorus uptake and such systems can be 
integrated into the larger environmental setting. 



XXlll 



CHAPTER 1 
INTRODUCTION 1 

A central question in ecological engineering is how to organize the hydrological 
cycle of the human economy symbiotically with that of the supporting ecosystems and 
geological substrate so as to maximize their joint performance. This dissertation reports 
the development and evaluation of an ecologically engineered wastewater interface 
between saline municipal wastewater and a tropical coastal zone with limestone substrate, 
mangrove wetlands, tourist beaches and coral reefs. Potential for this wetland system was 
evaluated by estimating its role in the water, nutrient, and emergy budgets of the 
emerging coastal economy. 

To achieve the performance observed in ecosystems in nature, an ecologically 
engineered system may need to be coupled to the geological setting and cycles as 
organized with groundwater. This project uses a human-assisted self-organization 
and structure to innovate a union of wastewater treatment with the larger ecosystem 
context. 

Ecological engineering seeks a symbiotic mix of man-made and ecological self- 
design that maximizes productive work of the entire system (including the human 
economy and the larger-scale environmental system). Allowing this process to self- 
organize may develop better adapted ecosystems that prevail because of their greater 
empower (Odum, 1991). By such minimal human manipulation and management, 



materials are recycled, efficiency is enhanced, costs are reduced, and ecological 
processes contribute more. 

An important application of ecological engineering is the design of interface 
ecosystems to handle byproducts of the human economy and to maximize the 
performance of both the human economy and natural ecosystems (Mitsch and Jorgensen, 
1991). 

Scientific Questions in Ecological Engineering of Wastewater 

Treatment and release of wastewater from coastal development in Quintana Roo, 
in the Yucatan Peninsula of Mexico, involve new scientific questions.. 
Wastewater Interface Ecosystems in the Tropics 

Tropical coastlines have dry and wet season properties, frequent hurricanes and 
high temperatures year-round. There has been increasing interest in using wetlands as 
interface ecosystems for wastewater treatment since early studies demonstrated their 
effectiveness at removal of nutrients and suspended solids. These included use of cypress 
swamps in Florida (Odum et al., 1977; Ewel and Odum, 1984) and peatlands in northern 
Michigan (Kadlec, 1979). 

Constructed wetlands using surface-flow or subsurface flow emergent vegetation 
or aquatic plant systems have gained increasing acceptance (Hammer, 1989; Mitsch and 
Gosselink, 1993; Reed et al, 1995). Since such natural or constructed wetlands are often 
limited by solar insolation and show increased rates of uptake in warmer climates, such 
systems may be expected to operate even more efficiently in tropical regions. In addition, 
wastewater interface ecosystems may benefit from the high species diversity found in 
tropical regions since diversity at the biotic and metabolic level increases the efficiency 



of ecosystems (Jorgensen and Mitsch, 1991). Plant diversity may benefit wastewater 
treatment by providing 1/ greater variety of root systems, allowing for greater penetration 
of the limestone gravel and supporting a wider range of associated microorganisms; 
2/differing metabolic needs (e.g. nutrient uptake) may lead to greater capacity for 
absorbing wastewater constituents; 3/differing seasonal cycles of activity which may 
increase plant productivity year-round; 4/ greater ability to utilize the full spectrum of 
incident solar radiation by the inclusion of shade-tolerant as well as top canopy species 
and 5/ differing "specialist" capabilities (e.g. C 3 and C 4 photosynthetic pathways, or 
quantity of aerenchyma tissue in saturated conditions) allowing for greater system 
response to changing environmental conditions such as light, heat, and nutrient levels. 
Greater diversity also buffers against system failure should disease or herbivory decimate 
selected plant species in the constructed wetland. There is evidence that allowing self- 
organization to develop cooperative mechanisms enhances the ability of adapted 
ecosystems to handle pollution and toxicity (Odum, 1991). 
Wastewater Interactions in Landscapes with Soil Substrate of Limestone 

Landscapes on limestone platforms offer special challenges and opportunities for 
ecologically engineered wastewater treatment. Calcium carbonate, the predominant 
mineral compound, has the ability to react with phosphorus and thus offers the potential 
for enhanced nutrient retention. On the other hand, such karstic landscapes are 
characterized frequently by relatively poor or shallow soil depth. In addition, the presence 
of rock such as limestone, which is dissolved by water, at ground surface permits rapid 
infiltration and lateral movement of wastewater (Bogli, 1980; Milanovic, 1981). 



Studies in similar subtropical and tropical limestone coastlines (e.g. the Florida 
Keys and Caribbean islands such as Jamaica) have indicated that they are especially 
susceptible to eutrophication through flow of septic tank effluent through porous 
calcareous strata since retention time does not allow for sufficient plant uptake or 
microbial decomposition (Bright et al, 1981; Pastorok and Bilyard, 1985). 
Salty Wastewater 

Wastewater with appreciable salt content has only rarely been studied in sewage 
treatment. It is an especially important vector in ecologically engineered wetland 
treatment systems as salinity is frequently a controlling factor in determining the types of 
organisms that will best self-organize such systems. In addition, salinity is important in 
coastal regions as groundwater salinity varies depending on factors such as tidal 
interchange, rainfall and evapotranspiration. Saltwater ecosystems such as estuaries, 
mangrove and salt marsh are amongst the world's most productive (Day et al, 1989). 
Previous work with mangroves (Sell, 1977) and with marine ponds receiving treated 
sewage have demonstrated their treatment effectiveness and capacity to self-organize to 
the input of eutrophic wastewater (Odum, 1985). 
Using Small-Scale Mesocosm Tests to Evaluate Regional Potentials 

The two small constructed wetlands (total area 130 m 2 ) evaluated in this research 
may be viewed as a mesocosm study of the impact of such interface ecosystems if more 
widely applied to the coastal regions of karstic tropical countries. A growing body of 
literature has demonstrated the applicability of such mesocosm studies to evaluate 
processes and potentials at higher spatial and energetic levels (Beyers and Odum, 1993). 
Frequently distinctive patterns of self-organization result from interface mesocosms 



exposed to extreme forcing functions such as high nutrient and hydrological subsidies 
(Odum, 1991) that can then be evaluated for scaling-up and application at regional levels. 

Problems of Fitting Water Systems to the Landscape 

Unique Characteristics of Tropical Coastal Development 

Over half the world's population live along coasts and adjoining rivers, and the 
rate of population increase in coastal areas exceeds those of inland regions (NRC, 1995). 
Especially in tropical developing countries, such issues have gained increasing attention 
due to recent accelerated growth of tourism and land development, exploitation of natural 
resources and the vulnerability of marine ecosystems, such as coral reefs, and coastal 
ecosystems, such as mangrove wetlands, to the effects of pollution and eutrophication 
(U.N., 1995). 

At present, lack of effective and affordable means of sewage disposal is 
widespread through the tropical developing world. This leads to chronic disease through 
human contact with polluted water and environmental damage to sensitive ecosystems. 
Coastal tourist development has been pursued by some developing tropical countries as a 
method of economic progress, utilizing their resources of warm climates, beautiful 
beaches and eco-tourism if they have attractive marine or terrestrial ecosystems. All too 
frequently, this tourist development exacerbates the problems of water contamination by 
placing large demands on available freshwater, adding new permanent and transient 
populations to an area, and converting land from natural ecosystems. 

Tropical areas are frequently characterized by extremely high biological diversity. 
The Yucatan, because of its tropical climate and isolation, has been able to sustain to date 
some of the most widespread and undamaged stands of tropical forest. The coastline 



around Akumal and this portion of the eastern Yucatan coast is an important breeding 
ground for loggerhead and green sea turtles, which come ashore annually to lay their 
eggs. 

In areas like the eastern Yucatan, the environmental hazard is especially great 
because of the highly permeable karstic geology and the presence of coral reefs offshore 
that are particularly sensitive to eutrophication. It is critical to not only evaluate current 
development, but to develop ecologically engineered solutions. The subsurface flow 
constructed wetlands, constructed as part of the present research effort in Akumal, will be 
evaluated as one strategy for sustaining water quality both for people and for 
environmental preservation in tropical coastal regions. 
Eutrophication Impacts on Coral Reefs 

Economic development results in the release of nutrients in coastal waters causing 
replacement of ecosystems such as coral reefs important to tourism. The impact of 
nutrients in coastal regions is greater than that of deeper waters because of the interplay 
between sediments and the water column, due to the strong vertical mixing by tidal 
currents and wind in the shallow water depths (Nixon and Pilson, 1983). Thus coastal 
regions are unlike deeper oceanic areas where deposited materials are "lost" to surface 
ecosystems. Thus coral reef ecosystems and other mature ecosystems are dependent on 
internal nutrient recycling for a large portion of their gross productivity (Laws, 1983), 
new growth requiring added nutrients. Nitrogen is sometimes a limiting factor for coral 
reefs (D'Elia and Wiebe, 1990), normally supplied by zooplankton captured by coral 
polyps. Excessive nutrients displace mature ecosystems with low diversity growths. 



Thus nutrient retention by the interface ecologically engineered wastewater wetland is an 
important criterion for maintenance of optimal environmental health at the higher level. 

A growing body of research indicates that coral reefs and other marine 
ecosystems such as seagrass can be rapidly degraded due to pollution from inadequately 
treated sewage. Seagrass ecosystems are normally mesotrophic and are vulnerable to 
shading, disease, and excessive epiphytic growth in eutrophied waters (Pastorok and 
Bilyard, 1985). Caribbean coral reefs, despite their high gross productivity, are adapted to 
oligotrophic waters where they maintain themselves using high nutrient retention and 
recycling. Corals are vulnerable to sewage pollution due to the following causes: 
1/ stress; 2/ decrease of available light and dissolved oxygen due to higher rates of 
sedimentation and enhanced growth of phytoplantkon and other microorganisms in the 
water column; 3/ overgrowth and bio-erosion of corals by fleshy macro-algae and benthic 
filter-feeding invertebrates that outcompete corals in high-nutrient waters; 4/ diseases 
resulting from bacterial growth stimulated by mucus-production by eutrophied corals; 
and 5/ direct chemical toxic effects (Hallock and Schlager, 1986; Pastorok and Bilyard, 
1985; Lapointe and Clark, 1992; and Hughes, 1994). 
Issues of Human Health 

Contamination of water resources is one of the leading causes of disease in 
tropical countries (U.N., 1995). Coastal areas with their shallower water tables are 
especially vulnerable to groundwater pollution. Water pollution includes pathogens 
carried by improperly treated sewage and potentially toxic chemicals. Pathogens include 
disease-causing bacteria, protozoa, viruses and helminths. Chemical hazards include 



8 

heavy metals, organic chemicals, and nitrates in sufficient concentrations to cause illness 
(Krishnan and Smith, 1987). 

Previous Studies 

Coral reef deterioration caused by eutrophication was studied in Kaneohe Bay, 
Oahu, Hawaii, which received sewage effluent from a treatment plant. In parts of the bay, 
coral loss stemmed from a buildup of organic matter, causing anaerobic conditions that 
released hydrogen sulfide, overgrowth from the explosive growth of "green bubbly 
algae" (Dictosphaeria cavernosa), sedimentation, and loss of light and competition by 
filter-feeders in increasingly turbid waters (DiSalvo, 1969; Laws, 1983; Grigg and 
Dollar; 1990). There was a proliferation of filter-feeders that bore into the corals. Benthic 
organisms outcompete water column plankton and filter-feeders in oligotrophic waters, 
but the reverse is true in nutrient-rich conditions (Laws, 1983). 

Previous studies of subsurface flow wetlands for sewage treatment have 
demonstrated their advantages in situations of small, on-site sewage loading in areas 
where land is scarce, or in situations where avoidance of malodor and mosquito-breeding 
are important (Kadlec and Knight, 1996). These are all the case in Akumal because of the 
high visibility of the treatment site, the need to create a nuisance-free and aesthetically 
attractive system, and the potential of a well-designed subsurface flow wetland of 
providing an inexpensive but highly effective degree of sewage treatment. As is the case 
in the U.S. and Europe where this approach is rapidly spreading, the advantages of 
constructed wetlands are that, because they rely on more natural methods, they are less 
expensive to build and operate than conventional sewage treatment plants 
(Tchonbanoglous, 1991). Constructed wetlands also can produce a standard of treatment 



equivalent to tertiary or advanced wastewater treatment. This is far better than a typical 
"package plant" or municipal sewage plant that produces effluent at secondary sewage 
standards quality, requires high capital investment and technical expertise and is energy- 
intensive (Reed et al, 1995). Subsurface wetlands use little or no electricity and 
technology and require little technical supervision once installed (Cooper, 1992, Steiner 
and Freeman, 1989; Green and Upton, 1992; Steiner, 1992). However, there is little prior 
research with these systems in tropical, karstic, coastal conditions. 

Wetland systems have long hydraulic residence times and through a variety of 
mechanisms (sedimentation, antibiotics, filtration, natural die-off etc.) have shown 
promise in achieving large reductions in coliform bacteria without the use of disinfectants 
like chlorine used in conventional sewage treatment (Reed et al., 1995). Chlorine has the 
potential to form toxic byproducts, such as chloramine, when released into marine 
environments (Berg, 1975). Bacteria can break down chlorinated hydrocarbons into 
compounds that may be far more dangerous than the original ones (Gunnerson, 1988), 
and sometimes de-chlorination has been required by regulatory agencies, further adding 
to the expense of such approaches (Kott, 1975). 

The dynamics of limestone in subsurface flow wetlands is also largely unknown. 
Theory suggests that limestone should increase phosphorus retention since calcium and 
magnesium are the primary agents of phosphorus fixation in alkaline conditions (Reddy, 
1997). A previous study with subsurface flow wetlands in Canada examined the efficacy 
of dolomite [CaMg (C0 3 ) 2 ] substrate containing 55% CaC0 3 . The substrate was found to 
be effective at removal of P in influent wastewater handling secondary wastewater, but 
when primary wastewater with higher P levels were used, P retention capacity proved 






10 

inadequate, and P-retention capacity decreased by 77% over 45 months of operation 
(Reddy, 1997). 

Study Sites in the Yucatan 

Regional Study Area: Akumal Coastline 

The research site is the coastal region around Akumal, Quintana Roo, Mexico 
(Figure 1-1), about 90 kilometers south of Cancun on the eastern coast of the Yucatan 
Peninsula, and 10 km north of the town and Mayan ruins at Tulum. Like many tropical 
coastlines, the eastern Yucatan is underlain by permeable limestone that, in a kilometer- 
wide area adjacent to the coast, is believed to be the remains of Pleistocene coral reef 
communities (Shaw, in press). The hydrogeology of the coastal region around our study 
site in Mexico was studied during the 1960s and 1970s (Ward and Weidie, 1976; Ward et 
al, 1985), and water budgets for the region were developed by Lesser (1976). 

In the northern third of the Yucatan (which includes the study site at Akumal), 
maximum elevation is about 40 m though most of the land surface is in a very flat plain 
of rough, pitted terrain, caused by weathering of the very permeable limestone, which is 
exposed over most of the surface. Because of the general absence of other sediments or 
soil, no surface drainage system exists. Cenotes (sinkholes) are the main bodies of fresh 
water, and almost all water movement is subsurface through the fractured limestone. 

Shaw (in press) has described the area's geologic profile and how the modern 
topographic features have been derived from their Pleistocene predecessors (Figure 1-2). 
About one kilometer inland is an Upper Pleistocene (Sangamon) beach ridge, with a 
maximum elevation of 8 m, which is segmented by triangular spits that extend up to 750 
m towards the sea. Modern, sandy, rounded bays have been formed by Holocene flooding 



11 



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Figure 1-1 Map of eastern Yucatan Peninsula of Mexico showing coastal area of study 
around Akumal, Quintana Roo, north of Tulum. 



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of the Pleistocene ones. Behind the headlands several hundred meters is a mixing zone 
where the mix of fresh and saltwater have led to dissolution of limestone, the collapse 
creating lagoons such as Yal-Ku in Akumal (Figure 1 -3). While this collapse has been 
attributed solely to the CaC0 3 solution kinetics in the mixing zone (Back et al, 1979), 
this area is associated with mangrove wetlands and biological activity may have been at 
least partly responsible for the limestone dissolution (Odum,pers. comm.). 

Akumal, which attracts tourists for its beaches, diving and snorkeling, has 
experienced growth, from dozens of permanent residents in 1970 to around 500 currently, 
with yearly tourist stays in the tens of thousands of days. There is evidence, from water 
quality monitoring done by the Centra Ecologico Akumal (CEA), that there is growing 
pollution of the terrestrial and marine environments. Shaw (1997) has documented a 
pollution plume in Akumal as high as 2000 coliform colonies/ 100 ml in groundwater. 
The finding of pollution correlates with the movement of this water through reef rock of 
high porosity and permeability (Figures 1-4, 1-5, 1-6). 

This pollution poses dangers both for people, due to contamination of 
groundwater supplies and recreational contact with improperly treated sewage, and for 
natural ecosystems such as the coral reef system offshore. Pollution and beach 
development also are of concern in the study area because the coastline around Akumal is 
an important breeding ground for leatherback and green sea turtles, which come ashore 
annually to lay their eggs. 
Growth and Development in the Yucatan 

The rapid growth of the Yucatan Peninsula as an international and Mexican 
tourist destination followed the selection of the area by the national government because 



14 





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Salinity, % SW 
October 21-22, 1994 




clnl , 5u C0 u! 0UrS m AkUma ' during a P eriod of no rain - Contours are 
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16 



Salinity, % SW 
May 16, 1995 



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17 




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18 

of its excellent beaches, beautiful off-shore coral reefs, and Mayan ruins. Cancun now 
receives over two million visitors per year and Quintana Roo close to three million 
annually. The entire population of the state of Quintana Roo was less than 25,000 in 
1950, but grew to around 200,000 by 1980 (Edwards, 1986). Evidence from tourism 
development in other countries indicates that intensity of negative environmental and 
cultural impact are related to scale (Jenkins, 1982, Rodenburg, 1980). 

The geology of the coastal area of the eastern Yucatan is one of extreme 
topographic flatness, underlain with carbonate rocks, predominantly limestone, of 
Tertiary age. The soil is generally shallow (0-20 cm deep), which, coupled with high 
permeability of the limestone, results in rapid infiltration of rain and high lateral 
movement. The result is a thin lens of groundwater (less than 70 m thick) overlying 
deeper groundwater that is close to the salinity of ocean water (Hanshaw and Back, 
1980). 

The Yucatan region is freshwater limited despite the ample rainfall (around 1 100 
mm of annual rainfall) and humid climate, and strategies for effective water utilization 
have characterized human settlement in the region since the time of the Mayan 
civilization (Back, 1995). These water limitations result from the nature of its almost pure 
limestone karstic geology without appreciable other sediments. When the limestone 
dissolves, forming solution depressions, these channels are not filled, so retain high 
permeability and porosity. This geology produces low hydraulic head, which results in 
restricted freshwater aquifers since the freshwater/saltwater interface is quite close to the 
ground surface near to the coast. The Yucatan also lacks rivers, except in its southern 
portions, because with the nearly flat topography of a coastal plain, and absence of 



19 

sediments, infiltration of rain to the water table is extremely rapid (Espejel, 1987). 
Seasonal variability of rainfall is considerable, which also limits freshwater availability. 
The region's high permeability not only decreases the amount of freshwater available, but 
also makes the water supply very vulnerable to contamination by sewage effluent, 
agricultural runoff, and the products of litterfall decomposition from the inland forests. 
The resulting pollution, exacerbated by tropical climate, which favors the growth of 
disease bacteria, is widespread in the Yucatan (Back, 1995). 
Sites of Mesocosm Tests 

Two subsurface flow wetlands for sewage treatment were constructed off the 
"main street" in Akumal to serve residences, offices and public toilets. These constructed 
wetlands are located about 250 m inland from Akumal Bay, and in close proximity (5-50 
m) to a natural mangrove wetland as can be seen in an aerial photo of Akumal (Figure 1- 
7), a topographic map of the study area (Figure 1-8) and sketch of treatment wetland units 
and mangrove areas of the study (Figure 1-9). Groundwater was encountered at less than 
1 m below ground surface during construction in August 1996. There is a thin layer of 
sandy soil (6-10 inches) below which limestone rock is encountered. 
Receiving Wetland 

The mangrove wetlands around Akumal are unusual in that most have a groundwater 
connection to seawater rather than having surface tidal channels. But like all mangrove 
ecosystems, their hydrologic and salinity environments are highly dependent on the 
relative and shifting predominance of freshwater and seawater that they receive. 
Productivity in mangroves typically increases as one moves from mangrove areas 



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23 

dominated by low-nutrient and high salinity seawater to ones enriched by freshwater 
nutrient inputs and with decreased salinity (Day et al., 1989). 

Mangroves have been shown to be effective in treating secondary wastewater. Sell 
(1977) studied two South Florida tidal mangrove ecosystems enriched by effluent from a 
sewage treatment plant. Mangrove growth was enhanced and there were no significant 
differences in species composition, seedling survival or litterfall between mangroves 
areas receiving enriched nutrient waters and control mangrove ecosystems. 

Soils in the Akumal region are characterized by low nutrient status. Noguez-Galvez 
(1991) studied nutrient levels near Carillo Puerto (19deg 16'N., 88 deg. 07' W) about 50 
km inland from the coast and 75 km south of Akumal after differing ages of fallow 
following slash-and-burn shifting agricultural use. Total N in the 0-5 cm layer was 0.437 
± 0.022% at 1 year fallow rising to 0.619 ± 0.095% after 20 years fallow. In the 6-1 1cm 
layer, the total nitrogen data were 0.316% ± 0.044% after 1 year, and 0.478 ± 0.076% 
after 20 years. Phosphate levels were 12.16 ± 1.75 mg/kg after 1 year in the 0-5 cm level, 
rising to 16.72 ± 4.61 mg/kg after 10 yrs, and 6.35 ± 2.35 mg/kg in the 6-1 1 cm level after 
1 year, and 1 1.33 ± 7.7 mg/kg after 10 years of fallow. 

At Puerto Moreles, Mexico, about 70 km north of the study site, Feller (1998) 
found autochtonous mangroves without external source of sediment, creating a highly 
organic peat substrate in the saturated subsurface. These soils are classified as solonchaks 
and histosols in view of their high organic content and salinity (McKee, 1998). The 
overall environment is oligotrophic and dominated by calcium carbonate limestone. 
Human impacts include road-making, clearing, diking, filling, and garbage dumping 
associated with tourist development. Road impoundments have not severed hydrological 



24 

connections since drainage is predominantly through groundwater connection with both 
fresh and saltwater. Trejo-Torres et al (1993) found that Yucatan coastal mangroves 
export freshwater during the rainy season and receive considerable seawater during drier 
periods. In Belize, south of the study site, mangroves were primarily phosphorus limited, 
and fertilization with phosphorus or a combination of nitrogen, phosphorus and 
potassium (but not with nitrogen alone) produced sizeable increase of growth in 
mangrove species (Feller, 1995). 

Mangroves were found in five zones along the Yucatan coast depending on 
distance from the coast. Highest biomass and basal areas were found in the mangrove 
zone closest to the coast (Feller, 1998), which is the zone receiving the experimental 
discharge of treated sewage effluent at Akumal. 

Concepts 

Aggregated Conceptual Model 

Figure 1-10 is an aggregated systems diagram of the treatment unit within the 
context of the coastal economy and environment. The sources of natural energy include 
sun, wind, rain, inland groundwater flow, and wave and tidal activity of the sea. 
Primary producing ecosystems are the inland forest, the mixed wetlands shaped by both 
freshwater and saltwater near the coast, and the marine ecosystems (seagrass, coral reef 
etc.). The human economy is supported by these natural ecosystems, local resources 
(limestone, forest products), and imported goods and services. Tourism is the principal 
source of monetary flow in the area; it pays for goods and services. The treatment 
wetland units make an interface between the wastewater produced by the human 






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economy before discharging treated water and nutrients to be recycled back into the 
mixed wetlands. 
Diversity vs. Trophic Conditions in the Interface Treatment System 

These ecologically engineered systems provided an opportunity to investigate issues 
of diversity vs. trophic state. Constructed wetlands have generally failed to maintain high 
species numbers and diversity. This failure has been attributed to high nutrient waters 
favoring the growth of species (such as Typha spp. or Phragmites spp.) that out-compete 
other, less aggressive species. In the United States and Europe, many constructed 
wetlands have not attempted to provide ecosystem attributes. They were designed as 
monocultures or planted with only 2-3 species, but have nevertheless provided 
satisfactory water treatment (Reed et al, 1 995). 

The relationship between nutrient status and species diversity is far from well 
understood. Yount (1956 cited in Odum, 1996) correlated pulses of nutrient enrichment 
with increased dominance, variation, competitive exclusion and loss or masking of rarer 
species. However, natural conditions of steady-state, high eutrophication have also 
promoted high diversity as contrasted to sudden conditions of eutrophication caused by 
anthropogenic pollution (Odum, 1996). Some types of human disturbance (e.g. fire, 
grazing and cutting in Mediterranean-climate Israel) enhance numbers of species 
(Naveh and Whittaker, 1979 cited in Mooney, 1986). 

Similarly, while the prevalent tendency is to regard high species diversification as 
a sign of ecosystem development toward maturity (Margalef, 1968), there are other 
circumstances in which high initial nutrient levels and species numbers are reduced as 



27 

storages are consumed (Odum, 1968), leading to suggestions that maximum species 
numbers may be maintained at intermediate successional stages (E.P. Odum, 1993). 
Ecological Succession in the Treatment System 

The research presented an opportunity to study ecological succession in the 
wetland mesocosms and to investigate some of the theoretical relationships posited for 
such self-organization. 

Odum (1994) noted that succession is the process by which structure and 
processes are developed by ecosystems from available energies and resources. These 
progressions often include system adaptation to physiological challenges, the building of 
storages, development of diversity and interchange with the larger, external 
environmental setting. 

Ecological succession typically includes a period of rapid initial growth 
dominated by aggressive, short-lived, pioneer species, giving way over time to species 
with high biomass and gross productivity but less net production. 

Among the characteristic patterns observed after system biomass and non-living 
organic matter have been increased and as primary succession gives way to a more 
mature, or equilibrium, stage are a greater balance between primary productivity and 
respiration. As succession proceeds, the more mature ecosystem tends to display greater 
internal cycling and retention of nutrients, increased specialization and mutualism, and 
increase of efficiency of use of input energy (E.P. Odum, 1971). 

The Akumal research offered an opportunity to track ecological succession and 
self-organization from an initial state of virtually lifeless quarried limestone gravel and to 



28 

track ecosystem changes that resulted from the input of domestic wastewater to an initial 
planting of wetland species. 

Major Objectives of the Research 

The major objectives of the present research were to develop a new, ecologically 
engineered wastewater treatment system and to evaluate its effectiveness and integration 
into the Yucatan coastal environment and human economy. Among the new elements 
under investigation were the efficacy of utilizing limestone gravel as the primary 
substrate for the constructed wetland, the ability of constructed wetlands with high- 
nutrient inputs to sustain a high level of biodiversity and devising an integration with the 
natural mangrove wetlands. In addition, evaluating whether the new treatment system 
was economically cost-effective compared to other approaches and whether its use of 
local resources (evaluated through emergy comparisons with other alternatives) would 
make it more sustainable for a tropical developing country than conventional sewage 
treatment options. Finally, if applied on a regional scale, to what extent would such a 
system retain the anthropogenically-produced nutrients which pollute groundwater and 
threaten the health of off-shore ecosystems such as coral reef? 






Plan of Study 



1 . Two pilot sewage treatment systems were constructed using saline influent wastewater, 
limestone gravel and multiple seeding of species on the eastern coast of the Yucatan. 

2. The living ecosystem was evaluated as it developed tracking species, diversity indices, 
percent cover, leaf area index, and transpiration estimated indirectly. 



29 

3. The water and nutrient budgets were evaluated by analysis of inflow waters and 
outflow waters, and a budget and simulation model that represents the seasonal cycle and 
role of the ecosystem were developed. 

4. After defining a representative square kilometer of coastal zone including tourist 
developments and their wastewater flows, the coastal water budget was evaluated. The 
role the new wastewater systems can have in the coastal water budget if expanded to 
service a kilometer of coastline was examined. 

5. The share of the system contributed by the environment and the economy was 
evaluated using emergy, transformity, empower and empower densities of the principal 
features of the wastewater unit and the main parts of the coastal area (hotels, people, 
substrate limestone, dollar circulation and exchange). 

Sampling and Measurement 

Periodic sampling of water quality was conducted for the septic tanks, wetland 
treatment compartments, groundwater and mangrove receiving wetland. Analysis was 
done in local Mexican laboratories (Alquimia, Cancun and Centra Ecologico Akumal) for 
parameters such as coliform bacteria and biochemical oxygen demand (BOD 5 ), which 
require immediate testing. Other parameters, such as phosphorus, nitrogen, suspended 
solids, and alkalinity, were tested in laboratories at the Water Reclamation Facility, 
University of Florida, Gainesville by Richard Smith, the laboratory manager. 

Bulk density and water-holding capacity for soils from the mangrove receiving 
wetland were conducted in the laboratory of the Centra Ecologico Akumal. Soil samples 
from the mangrove receiving wetland were analyzed for organic matter content and 
phosphorus and nitrogen content at the at the Institute of Food and Agricultural Sciences 



30 

(IF AS) Soil Testing Laboratory, Gainesville. Analysis for mineral composition of the soil 
was conducted using X-ray diffraction techniques by Dr. Willie Harris at the Pedology 
Laboratory of the University of Florida, Gainesville. 

Field measurements for ecological characteristics such as species number, cover 
and frequency were conducted during research visits to the study site. Identification of 
species were made with Edgar F. Cabrera, a biologist from Chetumal, Quintana Roo. 

Limestone from the system was collected before treatment began and after 1 1 
months of system operation. Analysis of the limestone for elemental composition was 
done at the IFAS Soils Laboratory, with the help of Dr. James Bartos. Analysis of 
limestone gravel for phosphorus was done at the University of Florida Wetland 
Biogeochemistry Laboratory with the help of its manager, Ms. Yu Wang. Experiments 
on limestone uptake of phosphorus were conducted at the same laboratory. 

Outline of the Research Report 

The research was reported in the following manner. Chapter 2 gives the 
methodology followed in all the components of the research. Chapter 3 presents results 
from the following areas 

a/ Ecological characterization of the limestone wetland ecosystem, including 
species number, biodiversity, frequency, cover, leaf area index, leaf holes, interception of 
sunlight, canopy closure and surface organic matter. 

b/ Wastewater treatment including total phosphorus, total nitrogen, biochemical 
oxygen demand, total suspended solids, salinity, alkalinity and uptake of phosphorus by 
limestone gravel, and water budget. 



31 

c/ Economic and emergy evaluation of the wetland treatment system and in 
comparison with an alternative conventional treatment approach. 

d/ Impact on the mangrove wetland including characterization of the hydrology 
and soil sediments of the ecosystem; and nutrient status of the soils and water before and 
after discharge of treated wastewater effluent from the limestone wetland unit. 

d/ Simulation of the water budget of wetland treatment system and mangrove. 

e/ Regional evaluation of application of the treatment wetlands. This was done by 
first assessing the emergy and monetary flows in a square kilometer of developed 
coastline, then evaluating the impact on this larger system's water and nutrient budgets 
with and without the use of the wetland treatment systems. 

Chapter 4 presents a discussion of the major findings of the present study, and 
commentary on important vectors in the new wetland system for treating domestic 
wastewater along the Yucatan coast. Observations are presented on the pattern of 
ecological succession, the role of limestone, and a simulation model is developed for the 
interaction of the environment and the tourist economy of the area. Finally, potential for 
future application of the system in the region is discussed and remaining questions for 
future research are listed. 

Appendix A contains water levels measured for the tide at Akumal, in the 
mangrove and in nearby cenote (groundwater well). Appendix B presents literature data 
used in the model. Appendix C contains the emergy evaluation of the University of 
Florida sewage treatment facility that is used for comparison to the limestone wetland 
system. 



CHAPTER 2 
METHODS 



Treatment Systems 

Ecological Engineering Design 

A constructed wetland for sewage treatment was developed meshing with the 
environmental/geological context of the Akumal coastline. Following the concept of 
ecological engineering, maximizing the work of natural elements, minimizing the use of 
machinery and reducing cost. A system of contained wetlands was used to treat septic 
tank discharge using gravity-flow, eliminating the need for electrical pumps (Figure 2-1). 

Because of the thin soil layer, high porosity of underlying limestone and high 
water table of the coastal settlements, an impermeable concrete liner prevented discharge 
of wastewater before adequate treatment could be accomplished. A two-celled system 
was used so that there was capacity to absorb torrential rains. 

Limestone gravel with 1/4 - 3/8 inch diameter was used in the system. The 
advantage of using smaller size gravel is that surface area and porosity is increased. 
However, the trade-off is that smaller limestone gravel may undergo greater danger of 
compaction and dissolution over time (Steiner and Freeman, 1989). Larger limestone 
rock (2-4 inch diameter) was used in the first and last meter of each treatment cell to 
minimize the danger of clogging near inlet and collector pipes. 



32 



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Outflows from the treatment wetlands were discharged into natural groundwater 
mangrove wetlands where there was natural filtering capacity of rich, organic soils and 
root uptake. 

The treatment wetland systems were built with financing and support from 
Planetary Coral Reef Foundation and the Centro Ecologico Akumal. Local Mayan 
contractors and laborers did the construction work. Local sources of limestone 
and sand were used. Public meetings in Akumal explained the planned research and 
provided updates on research findings to government, business and local residents. 
Procedures for Start-up and Management 

An initial layer of sawdust mulch was applied to the system over the limestone, 
establishing an aerobic layer for plants that could be sustained later by leaf litter drop. 

Maintenance guidelines called for minimal interference without pruning 
vegetation or eliminating species. Disease or pest pulses would be allowed, since these 
form a part of nature's diversity mechanisms. Monitoring allowed tracking of natural 
self-organization of introduced and volunteer plant species. 
Seeding with Biota 

The wetlands were planted with a wide variety of wetland plants, some 
transplanted from local wetland areas, some from local commercial plant nurseries, 
others from the botanical garden at Puerto Moreles and local gardens in Akumal. Some 
species entered the system as seeds carried in by wind or animals from nearby wetlands, 
as seeds or seedlings in the soil of plants transplanted from the wild, or during the 
construction process. 



35 

There was no attempt to limit species. None were removed manually as unwanted 
('weeds"). Trees and large palm species were planted at least 2 m away from the system 
piping to minimize maintenance problems with roots. Multiple rounds of seeding were 
arranged following experience with promoting self-organization in mesocosms (Beyers 
and Odum, 1993). 
Field Measurements 

Biodiversity 

Plant species richness was determined by identification of plant species in the 
wetlands with the assistance of Edgar Cabrera, Chetumal, Q.R., a botanist from the 
region. Transects of approximately 250 observations were conducted in each of the two 
treatment cells of the two wetland systems, giving a total of about 1000 observations. 
These observations were made in May 1997, December 1997 and July 1998. 
Comparisons with biodiversity of natural ecosystems in the region (mangrove and 
tropical inland forest) were done by conducting transects with 1000 individual plants, 
identifying each to species in December 1997. 

Biodiversity was calculated using the Shannon diversity index (Shannon and 
Weaver, 1949; Brower etal, 1991): 
H' = -2 p, log p, 
where p, = n/N 

"Pi" is the proportion of species "I" in the total number of individuals in the population 
(N). The Shannon biodiversity index was calculated using the above formulas for log 2 
and log 10. 






36 



Frequency 

Frequency is a measure of the probability of finding an individual species with the 
overall population sample (Brower et al, 1991). Plant species' frequency in the wetlands 
was determined by analysis of the transects. Each individual plant stem was counted as 
an observation in the transect. Data was tabulated for each treatment cell and cumulative 
data were tabulated for each wetland system, and data for the combined two wetland 
systems were analyzed. 
Cover 

Plant cover for each species was determined by 1/ use of 0.25 m 2 quadrats in each 
treatment cell and estimating percent cover of each species present, as well as percent of 
bare ground; 2/ measuring canopy cover of the most prevalent species (15-20) in each 
treatment cell (May 1997) and 3/estimating canopy coverage of all wetland species in 
each treatment cell (December 1997 and July 1998). 
Importance values 

Importance values (IV) were calculated combining frequency and cover data and 
dividing by two, so that the sum of all IV values for each system equaled one. These 
calculations were made using the May 1997, December 1997 and July 1998 field data. 
The graph of these data, called a dominance-density curve or species importance curve, 
was plotted on a log/arithmetic scale against rank order (Brower et al, 1991). 
Leaf area index 

Leaf area index was determined by the point-intercept method. Approximately 50 
measurements were made in each treatment cell of the wetland systems in May, 1997, 



37 






December 1997 and July 1998. Using a tall piece of steel rebar moved a set distance 
along pre-assigned transect lines, the number of leaves touching the pole were recorded. 
Each treatment cell had approximately 50 observations at each round of study. 
Leaf holes 

Holes in leaves due to herbivory, decomposition and other causes were measured 
in December 1997 and July 1998 by estimating percent leaf damage and loss on 5 
randomly selected leaves of each of the species present in the wetland. Then these data 
were multiplied by the relative frequency of each species to give an overall measure of 
leaf holes in the wetland systems. 
Surface organic matter 

Surface organic matter was determined by collecting surface litter from four 0. 1 
m quadrats within each cell of the two wetland systems in July 1998. Four samples of 
the original woodchip/sawdust mulch from 0. 1 m 2 quadrats from a similarly constructed 
wetland system in Akumal were collected to provide a measure of the starting surface 
organic matter of the wetlands. The surface litter was dried at 70°C and weighed, then 
combusted at 450°C in a muffle furnace of the Water Reclamation Laboratory 
of the University of Florida and reweighed. Organic matter content of samples was 
determined as the difference between starting and final weights. 
Solar insolation 

Solar insolation and light interception in the wetland systems was measured 
using a LI-COR LI- 189 Quantum/Radiometer/Photometer equipped with a LI-COR 
Terrestrial Radiation Sensor, Type SA (LI-200SA) pyranometer sensor. The pyranometer 









38 

was factory calibrated against an Eppley Precision Spectral Pyranometer under natural 
daylight conditions, giving an absolute error of ± 5% maximum, typically ± 3%. 
Quantum light measurement results were in umol s" 1 m 2 (1 umol s" 1 m 2 is equivalent to 
1 uEinstein s" 1 m" 2 ). 

Light measurements were conducted on 28 July 28 1998, a cloudless day, from 
1050 to 1 145 AM. Measurements were made of ambient solar insolation outside the 
wetland systems before and after measurements of each wetland cell. Approximately 30 
measurements were made in each of the 2 wetland cells of wetland system 1 and 50 
measurements in each cell of wetland system 2. Measurements were made 0.5 m in from 
the edge of each cell and then every 1 m across the cells. 
Canopy closure 

Canopy closure in the wetland systems was evaluated in July 1998 using 
analysis of hemispheric canopy photography (Rich, 1989). Photographic images of the 
wetland canopies were made using a 180° fish-eye lens adapter on a Nikon camera. Nine 
photos were taken at predetermined and equivalent locations in each of the wetland cells, 
and in the discharge area of the mangrove ecosystem, then digitized and converted to a 
gray scale using Photoshop 2.0. Analysis for amount of canopy and light penetration was 
done with MapFactory software. 



39 

Analytic Measurements 

Total nitrogen and total phosphorus 

To determine nutrient treatment in the wetlands of phosphorus and nitrogen, 
laboratory tests for total phosphorus and total nitrogen were conducted on wastewater 
samples from the wetland treatment systems. 

Phosphorus was determined using persulfate digestion followed by the ascorbic 
acid method, SM 4500-P (APHA, 1995). Tests were conducted at the University of 
Florida Water Reclamation Laboratory. Total nitrogen was determined using the 
persulfate method, SM 4500-N (APHA, 1995). 

Samples were collected from the septic tank, from the standpipe at the end of cell 
1 and cell 2 in each wetland treatment system. A sample was collected from a cenote 
(shallow groundwater well) with water accessible a few feet below ground level located 
just a few meters from the wetland treatment system. This cenote is located on the inland 
side of the wetland systems, and is presumed to give some indication of local 
groundwater background levels. After collection in a 10 ml sample bottle, 1-2 drops of 
concentrated sulfuric acid was added to preserve the samples until shipping to the 
laboratory. 

To determine variability in the total P and total N laboratory test, two samples 
were run three times in August and September, 1997 so that standard deviation and 
standard error of the mean could be determined. 



40 

Biochemical oxygen demand (BOD) 

Biochemical oxygen demand (BOD) was determined using EPA method 405.1 
(EPA, 1993). This is a five day test with sample kept at 20°C. Samples (250 ml) were 
collected as described above and kept cool during transport to the laboratory. The 
materials were tested in laboratories in Cancun. The tests from January to April 1997 
were conducted at Laboratorio Alquimia, Cancun and those from May 1997 were 
conducted at the laboratory of Jose Castro in Cancun. Both are certified laboratories for 
water analysis. 
Chemical oxygen demand (COD) 

Chemical oxygen demand in the water of the mangroves was determined 
using the closed reflux, colorimetric method, APHA 5220D (APHA, 1995). The sample 
was digested using K 2 Cr 2 7 , H 2 S0 4 , and HgS0 4 . Tests were conducted using Hach 
prepared reagants, and analyzed on a Hach DR-3000 colorimetric instrument at the 
laboratory of the University of Florida Water Reclamation Facility. 
Total suspended solids 

Total suspended solids (TSS) in the wastewater were determined using the 
filterable residue, a gravimetric method with the material dried at 180°C, EPA method 
160.1 (EPA, 1993), method 2540DSM (APHA, 1995). 250 ml. samples were collected 
from the seven points described above and stored for shipment to the Water Reclamation 
Laboratory, University of Florida, where the tests were conducted. 



41 

Fecal coliform bacteria 

Fecal coliform in the wastewater was determined using membrane filtration and 
most probable number (MPN) of colonies per 100 ml of sample. This is method 
9222DSM (APHA, 1995). Samples (175 ml) were collected from the seven points 
described above and transported to the laboratory in Cancun for analysis within hours of 
collection. The same laboratories that conducted the BOD-5 tests conducted the analyses 
for fecal coliform until May 1998, when analysis was conducted in the water laboratory 
of the Centro Ecologico Akumal. 
Alkalinity 

Alkalinity of the water samples was determined by titration (buret), method 
2320B (APHA, 1995). Samples weighed 50 ml and the method used .02 N sulfuric acid. 
Salinity 

Salinity of water samples from the septic tank and wetlands was determined with 
use of a hand-held refractometer accurate to +/- 0.5 parts salt per thousand. 
Phosphorus Uptake by Limestone 

Initial P content and uptake in wetlands 

Samples of limestone were analyzed for initial phosphorus content and 
phosphorus content after exposure to sewage in the treatment wetlands. Pre-exposure 
limestone was collected during construction and bagged for later analysis. In December 
1997 after one year of sewage treatment had occurred, composite limestone samples 
were collected from each of the treatment cells of systems 1 and 2. These were divided 
into limestone from the layer above the sewage line, and those at 0-10 cm depth, 10-20 



42 

cm depth, 20-30 cm depth, 30-40 cm depth and 40-50 cm depth. These limestone 
samples were roughly pulverized mechanically then ground in a ball grinder. 

Inorganic P analysis, conducted in the Wetland Biogeochemistry Laboratory at 
the University of Florida, was determined as follows. Following grinding, the limestone 
samples were dried in an oven at 70 deg.C. for 48 hours. Then a subsample (0.5 g) of the 
ground limestone was extracted with 25 ml of 1M HC1 for 3 hours, then filtered through 
a 0.45 micrometer pore size membrane filter. The HC1 extract was stored at 4°C in a 20 
ml polyethylene vial. The HC1 extract was analyzed for inorganic P using an automated 
ascorbic acid method (Method 365.1, EPA, 1995). 
Calcium/magnesium composition of Yucatan limestone 

The limestone was analyzed for calcium and magnesium content at the Soils 
Laboratory of the Institute of Food and Agricultural Sciences (IFAS), University of 
Florida. 

The procedure was to grind and dry samples of limestone in a 120°C oven for 4 
hours. Then 5 x 1.0 gram dried sample was placed in a 1000 ml graduated beaker, and. 
125 ml of IN HC1 solution was added to dissolve the limestone. The solution was diluted 
to 250 ml of 0.25M hydrochloric acid. The beaker was covered with a watch glass and 
boiled gently on hot-plate for 10-15 minutes. Condensate was washed into beaker with 
de-ionized filtered (D.I.) water and cooled to room temperature. The solution was 
brought to approximate volume of 1000 ml. with D.I water. Analysis for 
calcium/magnesium was by inductive coupled plasma spectroscopy. 



43 

Experiments on phosphorus uptake by limestone 

To determine reaction kinetic rates of the Yucatan limestone with respect to 
phosphorus, a series of lab and field experiments were designed. The experimental 
procedure to determine phosphorus uptake by limestone was to combine limestone gravel 
samples from the wetlands. Five hundred ml plastic bottles were filled with 
approximately 250 grams of limestone gravel. Bottles were then filled with 450 ml of 
phosphorus solution. This left some airspace below the neck of the bottles. 

For the laboratory experiment, there were 5 experimental treatments x 3 
replicates for a total of 15 bottles. The initial phosphorus concentrations were 5.6 mg 
P/liter, 1 lmg P/liter, 22 mg P/liter, 56 mg P/liter, and 1 1 1 mg P/liter. After addition of 
phosphorus solution, bottles were maintained with caps only loosely on, allowing air 
exchange. Bottles were shaken once a day. After 10 days, 10 ml. samples were taken and 
filtered through a 0.45 urn membrane filter at 1,2,4,6 and 10 days. Separate syringes and 
filter cases were used for each of the six treatments. Samples were stored in a freezer 
until analysis for soluble reactive phosphorus. 

For the field experiment, 3 x 500 ml. bottles with 250 grams of limestone gravel 
prepared at the same time as the laboratory ones, were loaded with 450 ml of actual 
wastewater from the septic tanks in Akumal, Mexico. Three bottles with 250 grams of 
limestone were filled with 175 ml of actual wastewater (to approximate the condition in 
the wetland treatment system that the sewage water covers the limestone). The bottles 
had 10 ml. samples taken and filtered through a 0.45 micrometer membrane filter at 
1,2,4,6, 10 and 30 days after loading. The samples were kept in a freezer until shipment 
to the University of Florida Water Reclamation Laboratory for soluble reactive 



44 

phosphorus analysis. Analysis for soluble reactive phosphorus used EPA Method 365. 1 

(EPA, 1995) 

Water Budget of the Wetland Systems 

In May 1997 and December 1997 the water budget of the wetland systems were 
determined by measuring inputs and outputs from the system. The only water inputs to 
the systems are effluent from the septic tanks and direct rain, as no surface runoff or 
groundwater enters the constructed wetlands. By draining the system 1 and system 2 
septic tanks, and then measuring rate of re-fill, it was possible to estimate hydraulic 
loading. 

System evapotranspiration was calculated by measuring the decline over time in 
the water levels of the standpipes in the control box at the end of each cell of the wetland 
systems (see Figure 2-3 of the construction blueprints). Water-holding capacity of the 
gravel used in the wetland was estimated by filling a known quantity (20 liter bucket) 
with the limestone gravel and then measuring the amount of water that the volume holds. 

The only outputs from the system are evapotranspiration and discharge from the 
outlet in the control box of cell 2. Thus, once the average daily evapotranspiration is 
calculated, the average discharge from the system may be estimated by difference from 
average input from the septic tanks. 
Economic Evaluation 

Data on construction and maintenance costs of the wetland and package plant 
sewage treatment systems were collected. Annual costs were estimated using expected 
lifetimes of system components. 



45 

Emergy Evaluation 

Comparative evaluations of the emergy involved in the wetland sewage treatment 
system and a conventional "package plant" sewage system were carried out using survey 
data on materials, labor, equipment used in constructing and operating the systems, plus 
data on natural resource flow in the area. From these, emergy evaluation tables were 
developed and emergy indices used to compare the sewage treatment systems. 

Receiving Wetland 

Biodiversity 

Biodiversity of the mangrove area receiving discharge from Wetland system 2 
was monitored for biodiversity before effluent began in December 1997. Biodiversity 
was determined by ten transects of 100 individual plants identified to species. Shannon 
diversity was then calculated from these data (see previous section). 
Mangrove Soils 

Depth of the mangrove soils in the vicinity of the wetland discharge was 
determined in December 1997 by driving a piece of 1/8 inch steel rebar into the soil until 
it struck rock. This was done in four directions, each 90 deg. from the next, from the 
center of the discharge, with 20 total observations, each made at 3 m intervals. An 
isopach map was generated from these data. 

Wet/dry weight of the mangrove soils was determined in December 1997 by 
drying five sample bags of 30 cm. deep soil cores at 70°C until no further weight loss 
was observed. Bulk density was calculated by taking five soil cores to a 30 cm depth and 
then determining wet weight and dry weight after drying in an oven at 70 °C until there 



46 

was no further weight loss. Five soil samples collected in December 1997 were analyzed 
by the Soil Laboratory of the Institute for Food and Agricultural Sciences (IFAS), 
University of Florida for total phosphorus and total nitrogen (using Kjeldahl method for 
N and the dry ash method for P) and total organic content (by loss on ignition method). 
These latter tests are described below: 

Loss on ignition test for soil organic matter determination (Magdoff et al, 1996) 
was used for soils with organic content greater than 6%. Five gram soil samples were 
placed in a pre-heated oven at 1 20°C for 6 hours. After cooling for 30 minutes, a weighed 
subsample of soil was placed in a beaker and placed in a muffle furnace set to 450 °C. 
for at least 5 hours. For this study, samples were left for 14 hours. After cooling to room 
temperature, final weight was recorded. Percent organic matter was determined by 
comparing final weight with initial weight of the soil samples. 

Total Kjeldahl Nitrogen (TKN) and dry ash method for phosphorus (Hanlon et al, 
1998) were used by the IFAS Soil Laboratory in nutrient analysis of the mangrove soils. 
In the TKN procedure, 0.5 g of soil is digested with 2.0 g of Kjeldahl mixture in a 
digestion tube. The mixture is wet with pure water and 0.5 ml of concentrated sulfuric 
acid is added. The tubes are placed on a preheated aluminum block digester at 150 deg C. 
for 0.5 hours then the temperature is increased to 250°C for 2 hours. One ml. of hydrogen 
peroxide is added by pipette in two steps of 0.5 ml. A glass funnel is placed over the tube 
and digestion continues for 2.5-3 hours. The tubes are removed from the digester and 
cooled, then the sides of the tubes are washed with 5-10 ml of pure water. After mixing 
with a vortex shaker, the digestate is moved to a 100 ml volumetric flask. Approximately 
20 ml of solution is filtered through a Roger's Custom Lab 720 into a 90 ml. plastic cup. 



47 

A filtered subsample is transferred to a 20 ml. plastic scintillation vial and refrigerated 
until analysis on the RFA (air-segmented, continuous-flow, automated 
spectrophotometer). Final step is analysis on the RFA calibrated with digested standards 
for total nitrogen. 

In the dry ash P analysis, 1 g of oven-dry soil is combusted in a 500°C muffle 
furnace to ash for a minimum of 5 hours. The ash is then moistened with 5 drops of 
distilled water and dissolved with 5 ml of 6.0M hydrochloric acid. After 30 minutes, the 
solution containing the ash is transferred to a 50 ml volumetric flask and brought to 
volume with pure water. A filtered subsample is transferred to a 20 ml. plastic 
scintillation vial and refrigerated until analysis on the RFA (air-segmented, continuous- 
flow, automated spectrophotometer). Final step is analysis on the RFA calibrated with 
digested standards for total phosphorus. 
Micro-analysis for soil composition 

The mineral portion of the mangrove soils was assessed using X-ray diffraction 
at the Soil Pedology Laboratory of the University of Florida. 

After soil samples were mixed, organic materials were digested by addition of 
sodium hypochlorite, 5.25% by weight, to cover the sample. After digestion for 20 hours, 
each sample was put through a 1 5 micrometer sieve into distilled water. The soil sample 
was centrifuged at 2500 RPM for 3 minutes and the supernatant liquid poured off. Then a 
1 M solution of sodium chloride was added, and the solution again centrifuged at 2500 
RPM and the supernatant poured off. Then de-ionized water was added to the solid 
materials, and centrifuged at 3000 RPM for 5 minutes. Some of the liquid was poured 
off, and oriented mounts were prepared for X-ray diffraction analysis by depositing 



48 

suspended materials onto porous ceramic tiles under suction. One of the tile mounts was 
treated with potassium chloride, and two with magnesium chloride. The KG and MgCl2 
were added four times, and pulled through the ceramic tiles by a suction device. Then 
each ceramic tile soil mount was rinsed with de-ionized water four times. To one of the 
MgCl 2 treated tiles, 30% glycerol was added. The clay tiles were then analyzed by X-ray 
diffraction. Samples were scanned from 2 to 60 degrees 20 using a computer-controlled 
x-ray diffraction system equipped with stepping motor and graphite crystal 
monochromator. Power was 35 kV and scanning rate was 2° 20 per minute. 
Nutrients 

Mangrove soil samples collected before and after discharge commenced, at the 
beginning of May 1998 and monthly from June to August 1998, were analyzed using the 
Total Kjeldahl Nitrogen and Dry Ash Phosphorus methods described above in the section 
entitled Mangrove Soil. Soil samples were collected at 1, 3, 5 and 10 meters east, west, 
north and south of the discharge point. Mangrove water samples collected in December 
1997 and April 1998 were analyzed for biochemical oxygen demand, fecal coliform, 
suspended solids, total nitrogen, total phosphorus, salinity and alkalinity using methods 
described in the section on Analytic Measurements. These tests were repeated after 
discharge commenced in May, and monthly samples were collected June, July, and 
August 1998 to ascertain changes in the nutrient and water quality status of the mangrove 
groundwater. 



49 

Hydrogeology 

Water in the mangrove site at Akumal exchanged through groundwater channels 
from below. There was no surface connection to the sea. Hydrologeological studies of the 
fluxes with the receiving area were made by comparing surface water levels with those of 
a nearby cenote (well) and the sea. This was done with a water level chart recorder of 
surface water height during May 1997, December 1997 and July 1998 

Direction of water flow in the area was determined from the heights of water in 
three polyvinyl chloride (PVC) pipes, 10 cm in diameter, placed 60 cm deep in the 
mangrove soils, which served as piezometers. Elevations were determined by use of 
manual water-tube levels. Location and directional orientation of the piezometers was 
determined with a surveying level. Water levels in the piezometers are equal to the 
elevation of the hydraulic head (Fetter, 1994). Flow lines were determined by 
triangulation of these data on a map of the potentiometric surface in the vicinity of the 
discharge outfall. A series of 5 PVC monitoring pipes were installed in December 1997. 
One pipe was installed 1 meter upstream from outfall of the discharge pipe from the 
wetland, and three other pipes were installed 1, 3 and 6 meters in the direction of water 
flowlines in the mangrove. The fifth monitoring pipe was installed 12 meters southeast of 
the discharge pipe, in the direction of the edge of the mangrove. 

Simulation Model of the Water Budgets 

Simulation models were developed for the treatment units and their discharge into 
the receiving wetland. This model followed the methodology outlined in Odum (1994) 
and Odum and Odum (1996). After selecting a system boundary, outside sources were 



50 

listed, from the environment and from the human economy. Relationships and pathways 
between system components were identified including exports from the system. 
Relationships were translated into energy language symbols and then into rate equations. 
After average values were put on the pathways and in storage symbols, coefficients were 
calculated with spreadsheet. A simulation program was written in BASIC and sensitivity 
studied with scenarios. Simulation runs were compared with field and literature data. 

Evaluating Potential of Wastewater System for the Coastal Zone 

Potential significance of the treatment system was studied by considering a square 
kilometer of developed coastal area operating the treatment system. Evaluations were 
done on two scales: the treatment systems and the square kilometer. 
Emergy Evaluation 

An emergy evaluation of the square kilometer area was made using data from 
published sources, data on use of natural resources and human services obtained from 
hotel owners, homeowners and residents, and from town maps showing density and 
layout of properties in the area. 

Emergy analyses followed methods developed by Odum and Brown (Odum, 
1996; Doherty and Brown, 1993; Brown and Ulgiati, in press). This was done by 
developing systems diagrams showing energy sources, system components, pathways of 
energy and material flow in the system, system outputs and depreciation/heat sinks. 
These systems diagrams were developed in three forms: detailed, aggregated and three 
arm diagrams. Then data was collected, using published and new data, on material and 
energy flows. 



51 

Transformities 

Emergy tables were compiled, using transformities for the items. Table 2-1 
presents the transformity values used in all the emergy evaluations of the present study. 
With these system relationships and data, indices to compare emergy flows of the 
environment with those of the natural environment are evaluated. Among the indices 
evaluated were the investment ratio, emergy yield ratio, ratio of nonrenewable to 
renewable resources and empower density. These emergy indices characterize the 
intensity and balance of environmental vs. developed resources (Odum, 1996). 
Economic Evaluation 

Economic impact on the square kilometer coastal area were compared for the use 
of treatment wetlands or conventional package plant treatment systems. These data were 
evaluated as a percentage of overall capital investment and yearly monetary flow. 
Regional Water Budget 

A regional water budget for a square kilometer of coastline in the study area was 
developed including precipitation, inflow of groundwater from inland, tidal exchange, 
evapotranspiration, pumped water and sewage. Budgets were compared for development 
with no sewage treatment and development with treatment by constructed wetlands. 
Regional Nutrient Budget 

Regional nutrient budgets were developed for the same scenarios - that of 
development of a square kilometer of the Akumal coastal region. Nutrient budgets for 
nitrogen and phosphorus were examined for the scenarios of full development without 
sewage treatment and with treatment by constructed wetlands. 



52 



Table 2-1 Transformities and emergy per mass used in this study. 



Item 


Transformity 


Emergy per mass 


Reference 




Sej/J 


Sej/gram 






solar emjoule/joule 


solar emjoule/gram 




Sunlight 


1 (by definition) 




a 


Wind, kinetic 


6.63 E2 




a 


Rain, geopotential 


8.888 E3 




a 


Rain, chemical potential 






a 


energy 


1.5444 E4 






Tide 


2.3564 E4 




a 


Waves 


2.5889 E4 




a 


Earth cycle 


2.9 E4 




a 


Wood 


3.49 E4 




c 


Groundwater 


4.8 E4 




a 


Gas 


4.8 E4 




a 


Motor fuel (liquid) 


6.6 E4 




a 


Primitive labor 


8.1 E4 




b 


Food 


8.5 E4 




c 


Hurricanes 


9.579 E4 




d 


Electricity (global average) 










1.736 E5 




a 


Agricultural and forest 


2E5 




c 


products 








Untreated wastewater 


5.54 E5 




f 


Concrete 




7.0 E7 


h 


Plastic products 




9.26 E7 


c 


Pulp wood 




2.75 E8 


e 


Sand 




1.0 E9 


a 


Limestone 




1.0 E9 


a 


Steel + iron products 




1.78 E9 


a 


Potassium chloride 




1.1 E9 


a 


Machinery 




1.25 E10 


£ 


a Odum, 1996 








b Odum and Odum, 1983 








c Brown etal., 1992 








d Scatena et al., in press 








e Christiansen, 1984 








f Green, 1992 








g Odum etal., 1983 








h Brown and McClanahan, 1992 









CHAPTER 3 
RESULTS 

Treatment Mesocosms 

Design and Operation of the Wetland Units 

In August 1996, the two wetland sewage treatment systems were constructed. 
One, henceforth referred to as "wetland system 1" was designed to treat the wastewater 
of 16 people and covers an area of 50.6 m 2 . The second, "wetland system 2", designed to 
handle the sewage of 24 people, has an area of 81.2 m 2 . 

The treatment process for each wetland begins with a well-sealed two-chamber 
septic tank which receives wastewater from the residences and offices by gravity flow. 
Solids settle out in the septic tank which serves as primary treatment, and the 
commencement of microbial treatment of the sewage. A filter at the discharge pipe from 
the septic tank ensures that no solids larger than 1/64 inch can enter the wetland. Effluent 
from the septic tank overflows by gravity feed into a header pipe which distributes the 
sewage along the total width of the first of two treatment cells (compartments) of the 
constructed wetland. 

These wetlands were designed as subsurface flow systems, and have a cement 
liner and sides to prevent movement of untreated sewage into the groundwater. They 
were filled with limestone gravel to a depth of 0.6 m. Each cell of the wetland has a 
collector, perforated 4 inch PVC pipe at the end which direct wastewater into the 



53 



54 

centrally-located control box. Inside the control box, an adjustable standpipe determines the 
level at which wastewater is maintained in the wetland, as wastewater overflows its 
open end either from Cell 1 into the header pipe for Cell 2, or from Cell 2 to final discharge. 
Normally, the standpipe is fully vertical at a height of 55 cm. The wastewater is kept 5 cm 
below the level of the gravel. The sides of the system are at least 15 cm above the top of the 
gravel to allow for natural litter buildup and to prevent overflow in heavy rains. The terrain 
was graded to preclude surface water runoff inflow into the wetland systems. Hydraulic 
residence with design loading is 5-6 days depending on seasonal evapotranspiration. 

After the cement liner was completed, the system was filled with water and leak- 
tested. Then the gravel was added and leveled. Larger limestone rock (5-10 cm) was used 
in the first and last meter of each cell, around the header and collection pipes, to minimize 
the dangers of clogging. After the addition of the gravel, the systems were filled with 
tapwater and planted with wetland plants gathered from nearby wetlands, or purchased from 
botanical gardens or commercial plant nurseries in the area. Soil was not introduced into the 
system, except for rootballs of the plants. The plants were planted with at least 2-5 cm. 
contact with the water. After planting, the two wetlands were mulched with 2-4 cm sawdust. 

After discharge from Cell 2 of the wetland, the wastewater from System 1 enters 
perforated drainage pipes that slope away from the wetland. The trenches in which these 
pipes were laid were back-filled with limestone gravel to prevent clogging by dirt. System 2 
effluent is sent to the nearby mangrove wetland and discharged near soil surface. 

The blueprint drawings (Figures 3-1 to 3-10) show additional details of the 
construction. Limestone gravel depths were increased for wetlands built subsequently to this 
research in the area were done to a design specification of 80 cm to increase hydraulic 



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65 

retention time, rather than the 60 cm of limestone used in the two research wetlands of this 

study. 

Ecological Characteristics 

Patterns of biodiversity and dominance 

In May 1997, December 1997 and July 1998 (nine, fifteen and twenty-three months 
after planting, respectively) examinations of the wetland systems for species diversity was 
conducted with the assistance of Edgar Cabrera, a botanist from Chetumal, Quintana Roo. A 
total of 68 species were identified in May 1997, 70 species in December 1997 and 66 species 
in July 1998 (Table 3-1). Species native to the Yucatan constituted 47 of the 66-68 species 
present in May, 1997 and December 1997, with the remainder being cultivated and 
introduced species. 

Plant species richness (total number of species present) in each treatment cell 
decreased slightly over the course of the study as shown in Figures 3-11, 3-12 and 3-13. For 
example System 1 Cell 1 had 41 species in May 1997, 37 species in December 1997 and 35 
species in July 1998; while System 1 Cell 2 had 37 species in May 1997, 35 species in 
December 1997 and 36 species in July 1998. In May 1997, wetland System 1 averaged 39 
plant species per cell, in December 1997 and July 1998, the average was 36 species. 
Wetland System 2 averaged 47 species per cell in May 1997, 45 species in December 1997 
and July 1998. 

Considering the systems as a whole, in May 1997 there were 63 species in System 2 
(with 482 observations), 17% higher than in wetland System 1 with 54 species (from 482 
observations) (Figure 3-14). By December 1997, plant species had declined by about 10% in 



66 



Table 3-1. Plant species in the treatment wetlands from surveys of May, 1997, December, 
1997 and July, 1998. Total number of species as of May, 1997: 68 species; as of December, 
1997: 70 species, as of July, 1998: 66 species. 





Scientific Name 


Common Name 


Notes: N = Native, I = 








Introduced; C= Cultivated 


D2 


Acalypha hispida 


Cola de gato; cat's 
tail 


C; red cattail flowers 




Acrostichum danaefolium 


Helecho 


N; wetland fern, to 3 m 




Ageratum littorale 




N: blue-flowering little shrub 
(purplish flowers); annual 




Alocasia macrorhiza 


Mafota; elephant 


I; starchy root, very shiny 






ears, taro 


Large leaves; leaf is straighter 
and flatter than Xanthosema 


N2 


Aloe vera 


Sabila 


C; 


N2 


Alternanthera 
ramossissima 




N 


Dl 


Angelonia angustifolia 




N; delicate shrub, purple 
flowers 




Anthurium 


Moco de povo 


N; epiphyte 




Schlechtendalii 






Nl 


Anthurium sp. 




N 




Asclepias curassavica 




N; orange and yellow flowers 


Dl 


Bambusa sp. 


Bambu; bamboo 


i; 




Bidens pilosa 


Margarita 


N; yellow or white flowers 
(like daisy) 




Bravaisia tubiflora 


Sulub 


N; pink flowers like bells 




Caladium bicolor 


Bandera 


C; decorative taro 




Carina edulis 


Platonillo; canna 
lilly 


I; yellow flowers 


N2 


Capraria biflora 


Claudiosa 


N 




Carica Papaya 


Papaya 


N; edible fruit 


Dl 


Cestrum diurnum 


Galon de noche 


I; shrub/tree CEA Cell 2, long 
thin leaves 




Chamaedorea Seifrizii 


Palma camedor 


N; palm 




Chamaesyce 




N; delicate shrub with tiny 




hypericifolia 




white flowers 




Chrysobalanus icaco 


Icaco 


N; woody, sturdy shrub with 
thick leaves 


Nl 


Cissus sicyoides 




N; 




Cissus trifoliata 




N; vine, elongated, ovate 








leaves 




Citrus Aurantium 


Naranja agria; 
orange tree 


C; edible fruit 



67 



Scientific Name 

Coccoloba uvifera 

Conocarpus erecta 

Corchorus siliquosus 

Cordia sebestena 

N2 Crinum amabile 

Dl Cucumis melo 

D2 Cyperus ligularis 

Nl Delonix regia 

Nl; Desmodium incanum 

D2 

N2 Desmodium tortuosum 

Distichlis spicata. 

Dl Ecliptaalba 

Eleocharis cellulosa 
Dl Eleusine indica 

Eupatorium albicaule 



Common Name 

Uva de mer; sea 
grape 

Botoncillo; 
buttonwood tree 



Siricote 

Lidio reina 
Melo; melon 
Zacate cortadera 
Poinsettia 



Spike reed grass 



Notes: N = Native, I = 
Introduced; C=Cultivated 

N; beach tree, prostrate or 

upright 

N; mangrove area tree 

N; woody shrub, long-hard 

seed pods (tree) 

N; tree with large leaves, (next 

to Eleocharis CEA Cell 2) 

C 

I; melon vine 

N; 

C; 

N; 3-leaved leguminous vine 

N 

N; grass 

N; like botoncillo with dots on 

leaves; 

N; short wetland reed 

N; 

N: 2 notches on leaves nearer 

base 



Dl 


Euphorbia cyathophora 




N; 


Dl 


Eutachys petraea 




N; grass with "feathers" on 
ends 




Flaveria linearis 




N; yellow flowers 




Hymenocallis littoralis 


Lirio/Spider lilly 


N; white flowers; 


Nl 


Ipomoea indica 


morning glory 


N; vine with heart-shaped 
leaves 




Ipomoea Pes-caprae 


rinonina 


N;vine, morning glory family 


Nl; 


Iresine celosioides 




N; flowers are scales 


D2 










Ixora coccinea 


Ixora 


I; yellow or orange flowers, 
low shrub 




Kalanchoe pinnata 




I; 


Dl 


Lactuca intybacea 


Milk weed 


N; CEA Cell 1 


D2 


Lantana involucrata 


oregano xiru 


N; small flowering shrub, 
woody shrub; small serrations 








on leaves; succulent; fragrant 
leaves 


N2 


Leucaena glauca 




C 



68 





Scientific Name 


Common Name 


Nl; 


Lochnera rosea 


Teresita 


D2 






Dl 


Ludwigia octavalis 




Dl 


Lycopersicum esculenta 


Tomate; tomato 


D2 


Melanthera nivea 




N2 


Mimosa sp. 






Malvaviscus arboreus 


tulipancillo 




Musa sp. 


Platano; banana 




Nerium oleander 


Oleonder; oleander 


Nl 


Nopalea cochinillifera 


Napolito 




Paspalum virgatum 


Sacate 




Pedilanthus 






tithymaloides 




Nl; 


Pelliciera alliacea 




D2 


Philodendron sp 
Phyla nodiflora 





N2 Phyllanthus niruri 

Pluchea odorata 
D 1 Porophyllum punctatum 

Dl Portulaca oleracea 

Psychotria nervosa 
Rabdadenia biflora 

N2 Rhizophora mangle 
Rhoeo discolor 

Sansevieria triasiate 
Scindapsus aureus 

Nl; Selenicereus Donkelaarii 

D2 

Senna biflora 



Dl Sesbania emerus 



Santa Maria 



Verdolaga; moss 
rose 



Red mangrove 
Platonillo morado; 

Lengue de suegra 
Telefono 



Modrecacao 



Notes: N = Native, I = 
Introduced; C=CuItivated 

C; lavender flowers 

N; yellow flowers 

I; tomato plant 

N; small button-white flowers 

on sprawling shrub; 3-lobed 

leaves 

N 

N; red flowers, tree 

C; edible fruit 

I; pink flowers, small tree 

C; cactus; used as food 

N; sharp-leaved clump grass 

I; 

N; long stalk, delicate flower 

N; 

N: red stems, white flowers, 

sprawling shrub with sharp 

notches near tip of leaves, 

deep-grooved veins 

N 

N; purple flowering shrub 

N; decorative black dots on 

leaves, shrub, small leaf 

N; various colors 

N; 

N; "mangrove-like" vine CEA 

Cell 2 

N 

N; purple and green leaves, 

roseatte form 

C; small agave-like 

C; variegated leaves 

N: viney, thin cactus 

N; tree with rounded leaves; 
with a bunch of small, varied 
colored flowers 
N; tree with leguminous leaves 



69 



Scientific Name Common Name Notes: N = Native, I = 

Introduced; C=Cultivated 

Sesuvium portulacastrum Verdolaga de playa; N; beach succulent 

succulenta 

N; 

N; red berries like small 

tomatoes 

N; palmate leaves, 5-folias 

C; corner PCRF Cell 1 nr 

septic tank; tree 

N; palm, used for thatching 

N; to 3-4 m 

N; vine, 3-leaves, purple 

flowers 

N; yellow flower otherwise 

similar to V. elegans (77) 

N 

m C: palm tree; sharp thorns on 
fronds 

N; vine, yellow flowers 
N; starchy root; soft-leaved and 
more curved leaf form of taro 
C; purple flowering shrub 
C; thin, short blades, grass-like 
with pink flower 



Dl 


Solanum erianthum 






Solarium Schlechtendalii 




Nl; 


Syngonium sp. 




D2 








Terminalia Catappa 


Almendro 




Thrinax radiata 


Chit 




Typha domingensis 


Tule; cattail 


Nl: 


Vigna elegans 




D2 






Nl 


Vigna luteola 




Nl; 


Viguiera dentata 




D2 








Washingtonu robusta 


Washingtonii 


Nl 


Wedelia trilobata 






Xanthosoma roseum 


mafata; taro, 
elephant ears 



Zamia purpuraceus 
Nl Zephyranthes Lindleyana 



Plant species identified by Edgar F. Cabrera, Chetumal, Q.R. on surveys in May and 
December 1997, and July 1998.Code for column 2, Dl = dead or not found in December 
1997 survey but present in May, 1997 survey; Nl = new in December 1997 survey; D2 = 
dead or not found in July, 1998 survey, N2 = new in July 1998 survey. 



Botanic names: Cabrera, Martinez (1987), UNAM (1994), Brummitt (1992). 



70 



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74 

the individual wetlands (Figure 3-15) although overall number of species present in both 
wetlands increased slightly (from 68 to 70 species). Many of the species no longer present 
were low, understory shrubs, while almost half the newly present species were native vines. 
In July 1998, System 1 lost an additional 10% of species, with a total of 44 species, 
while System 2 remained constant at 57 (Figure 3-16), although again both numbers included 
a loss of some previously present species and establishment of new species (Table 3-1). 
Comparison with natural ecosystems 

In December 1997, transects with 1000 observations showed 73 species present in the 
inland tropical forest ecosystem, and 1 7 species in the natural mangrove wetlands, compared 
with the 70 species found in the constructed wetland treatment systems (Figure 3-17). Table 
3-2 lists the species found in the mangrove and Table 3-3 presents the species found in the 
forest ecosystem. Figure 3-18 compares number of species in treatment wetland systems 1 
and 2 with number of species found in the transects through forest and mangrove ecosystems. 
The wetlands had diversity of plant species comparable to that found in nearby forest 
ecosystems and a much greater number of species than were found in the adjacent mangrove 
wetlands. 
Dominance 

Dominance was assessed through species relative frequency, Shannon diversity 
index, percent cover, estimate of areal coverage and importance value. 



75 






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78 

# 

Table 3-2 Species list: mangrove wetland ecosystem, 8 December 1997. Species identified 
by Edgar Cabrera, Chetumal, Q.R. 

Name of Species 
Acrostichum danaefolium 
Anthrurium Schlectendalii 
Chlorophora tinctoria 
Conocarpus erecta 
Cyperus ligularis 
Diospyros cuniata 
Enriquebeltrania cientifola 
Ipomoea indica 
Laguncularia racemosa 
Piendia aculeata 
Rhabdadenia biflora 
Rhizophora mangle 
Selenicereus Donkelaarii 
Selenicereus testudo 
Solanum Schlechtendalii 
Thrinax radiata 
Yithecellobium dolle 

Botanic names: Cabrera, Martinez (1987), UNAM (1994), Brummitt (1992). 






79 



Table 3-3 Species list of inland forest near Akumal, Q.R., 9 December 1997. Species 
identified by Edgar Cabrera, Chetumal, Q.R. 



Species Name 

Acacia Collinsii 
/Acacia dolycostachia 
Acacia Gaunter i 
Acacia pennatula 
Amyris elemfera 
Anthurium Schlechtendalii 
Astronium graveoleus 
Ayenia pus ilia 
Bauhinia divaricata 
Beaucarnea ameliae 
Bromelia alsodeii 
Brosimum Alicastrum 
Bursera Simaruba 
Caesalpinia Gauneri 
Calocarpum acuminata 
Cenchrus ciliaris 
Chamaedorea Seifrizii 
Coccoloba acapulcensis 
Coccoloba diversifolia 
Coccoloba spicata 
Coccothrinax readea 
Dactyloctenium aegypticum 
Desmodium inconun 
Digitaria decumbens 
Diospyros veracruzensis 
Drypetes lateriflora 
Eleusine indica 
Esenbeckia Berlandieri 
Galactia striata 
Gouania lupuloides 
Grass sp. 

Gymnopodium florib undun 
Helicteris baruensis 
Hevea obovata 
Hompea trilobata 
Ichnanthus lanceolatus 
Jacquemontia nodiflora 



Species Name 



Karwinskyia Humboldtiana 
Lantana camara 
Lesaea divericata 
Malpighia amarginata 
Malvaviscus arboreus 
Manilkara zapodilla 
Melanthera nivea 
Melochia tomentosa 
Microgramma nitida 
Neea tenuis 
Ocimum micranthum 
Olira yucatana 
Oncidium sp. 
Otopappus guatemalensis 
Parthenium hysterophorus 
Paullinia pinnata 
Petrea volubilis 
Phyllanthus macriorus 
Piendia acileata 
Piscidia piscipula 
Plumeria obtusa 
Priva lapulacea 
Psychotria nervosa 
Sebastiania adenophora 
Selenicereus testuda 
Senna racemosa 
Sida acuta 

Spermacoce tetracera 
Talisia olivaeformis 
Themeda microntha 
Thevetia Gaumeri 
Thouinia paucidentata 
Thrinax radiata 
Unknown vine 
Veronia cinerea 
Vitex Gaumeri 



Botanic names: Cabrera, Martinez (1987), UNAM (1994), Brummitt (1992). 









80 



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81 

Shannon diversity index 

Shannon diversity indices for the wetlands (Table 3-4) confirmed that there was 
relatively high diversity in both constructed wetlands. In May 1997, wetland System 2 with a 
with a Shannon diversity of 4.59 (base 2), 1.38 (base 10) was higher than wetland System 1, 
whose diversity was 4.17 (base 2), 1.25 (base 10). However, by December 1997, their indices 
were far closer, with System 1 at 4.52 (base 2) and 1.36 (base 10) and System 2 at 4.49 (base 
2) and 1.35 (base 10). In July 1998, Shannon diversity had increased and remained very 
similar between the two wetland systems. Wetland System 1 had an index of 4.81 (base 2) 
and 1.45 (base 10), while wetland System 2 had a diversity index of 4.85 (base 2) and 1.46 
(base 10). 

Comparing the treatment wetlands with the nearby natural ecosystems (Table 3-5) 
shows that the tropical forest ecosystem was about 7% more diverse since it had a Shannon 
diversity index of 5.35 (base 2) and 1.61 (base 10). On the other hand, the constructed 
wetlands were far more diverse than the natural mangrove wetlands, which had a Shannon 
diversity of 1.49 (base 2) and 0.45 (base 10), only about 30% that of the treatment wetlands. 
Plant cover 

Calculation of species cover in each wetland treatment cell is shown in Table 3-6, 
Table 3-7 and Table 3-8. These observations demonstrate that overall plant coverage was 
higher in the first treatment cells of both wetland systems in May 1997. Plant cover in 
wetland System 1, Cell 1 averaged 85% compared to 74% in Cell 2, and in wetland System 
2, Cell 1 plant cover averaged 91%, while in Cell 2, plant cover was 48% of ground surface 
in the quadrats. By December 1997, coverage was equal between cells 1 and 2 of wetland 



82 



Table 3-4 Shannon diversity indices for constructed wetland systems based on May 1997, 
December 1997 and July 1998 surveys. 



Wetland location Date Shannon diversity Shannon diversity 

index, base 10 index, base 2 



System 1, Cell 1 May 1997 1.22 4.06 

December 1997 1.26 4.19 

July 1998 1.36 4.52 

System 1, Cell 2 May 1997 1.29 4.27 

December 1997 1.32 4.39 

July 1998 1.42 4.71 

System 2, Cell 1 May 1997 1.42 4.72 

December 1997 1.26 4.19 

July 1998 1.43 4.74 

System 2, Cell 2 May 1997 1.35 4.47 

December 1997 1.29 4.27 

July 1998 1.36 4.52 

System 1 (whole) May 1997 1.25 4.13 

December 1997 1.36 4.52 

July 1998 1.45 4.81 

System 2 (whole) May 1997 1.38 4.58 
December 1997 1.35 4.49 
July 1998 1.46 4_85_ 



83 



Table 3-5 Comparison of Shannon diversity indices for constructed wetlands vs. natural 
mangrove and tropical forest ecosystems of the study area, based on December 1997 and July 
1998 survey data. 



Ecosystem Shannon diversity, Shannon diversity, 

base 10 base 2 



Constructed wetland System 1 


1.45 


4.81 


Constructed wetland System 2 


1.46 


4.85 


Both constructed wetlands 


1.51 


5.01 


Mangrove ecosystem 


0.45 


1.49 


Tropical forest ecosystem 


1.61 


5.35 


















84 



Table 3-6 Relative cover in the wetland system cells, based on 0.25 sq m quadrat 
analysis, May 1997. 



Wetland system and 


Plant species 


Relative cover 


Rank 


cell 




by species 




System 1 Cell 1 


Carina edulis 


37.3% 


1 




Sesuvium portulacastrum 


12.6% 


2 




Typha domingensis 


11% 


3 




Alocasia macrorhiza 


9.5% 


4 




Paspalum virgatum 


8.7% 


5 




Solarium erianthum 


8.2% 


6 




Nerium oleander 


6.5% 


7 


System 1 Cell 2 


Canna edulis 


25.2% 


1 




Melanthera nivea 


12.2% 


2 




Hymenocallis littoralis 


9% 


3 




Sesuvium portulacastrum 


8.4% 


4 




Washingtonii robusta 


8% 


5 




Chrysobalanus icaco 


5.5% 


6 




Cyperus ligularis 


4.6% 


7 


System 2 Cell 1 


Canna edulis 


13.8% 


1 




Typha domingensis 


13.1% 


2 




Pluchea odorala 


9.7% 


3 




Sesuvium portulacastrum. 


9% 


4 




Ipomoea Pes-caprae 


6.6% 


5 




Ageratum littorale 


6.2% 


6 




Eleocharis cellulosa 


5.9% 


7 


System 2 Cell 2 


Canna edulis 


28.7% 


1 




Typha domingensis 


17% 


2 




Nerium oleander 


12.9% 


3 




Sesbania emerus 


8.8% 


4 




Solanus erianthum 


7% 


5 




Eleocharis cellulosa 


6.4% 


6 




Paspalum virgatum 


4.7% 


7 (tie) 




Alocasia macrorhiza 


4.7% 





85 



Table 3-7 Estimates of area coverage, including canopy, of dominant plants in the wetland 
treatment cells, May 1997. Total area of each cell in System 1 is 25.3 square meters, and area 
of each cell in System 2 is 40.6 square meters. 



Wetland system and 


Plant species 


Total 


Percentage of 


Rank 


cell 




coverage 
(m2) 


total area 




System 1, Cell 1 


Carina edulis 


5.35 


20.9% 


1 




Typha domingensis 


2.95 


11.7% 


2 




Alocasia macrorhiza 


1.58 


6.2% 


3 




Solatium erianthum 


1.1 


4.3% 


4 




Xanthosema roseum 


0.8 


3.2% 


5 (tie) 




Musa sp. 


0.8 


3.2% 






Phyla nodiflora 


0.6 


2.4% 


7 




Pluchea odorata 


0.5 


2% 


8 (tie) 




Conocarpus erecta 


0.5 


2% 




System 1, Cell 2 


Carina edulis 


3.95 


15.6% 


1 




Washingtonii robusta 


3.15 


12.5% 


2 




Cyperus ligularis 


2.2 


8.7% 


3 




Hymenocallis littoralis 


2.1 


8.1% 


4 




Typha domingensis 


1.9 


7.5% 


5 




Acrostichum danaefolium 


0.9 


3.6% 


6 




Ipomoea Pes-caprae 


0.8 


3.2% 


7 




Sesuvium portulacastrum 


0.7 


2.8% 


8 


System 2, Cell 1 


Typha domingensis 


4.85 


11.9% 


1 




Canna edulis 


3.73 


9.2% 


2 




Sesuvium portulacastrum 


2.5 


6.2% 


3 




Nerium oleander 


2.45 


6.1% 


4 




Washingtonii robusta 


1.9 


4.7% 


5 




Pluchea odorata 


1.75 


4.3% 


6 




Ageratum littorale 


1.6 


3.9% 


7 




Phyla nodiflora 


1.4 


3.4% 


8 


System 2, Cell 2 


Typha domingensis 


8.25 


20.3% 


1 




Canna edulis 


3.75 


9.2% 


2 




Solanum erianthum 


3.0 


7.4% 


3 




Eleocharis cellulosa 


1.5 


3.7% 


4 




Sesbania emerus 


1.15 


2.8% 


5 




Sesuvium portulacastrum 


1.0 


2.5% 


6 




Nerium oleander 


0.95 


2.3% 


7 




Alocasia macrorhiza 


0.5 


1.2% 


8 (tie) 




Musa sp. 


0.5 


1.2% 





86 



Table 3-8 Estimates of area coverage, including canopy, of dominant plants in the wetland 
treatment cells, December 1997 and July 1998. Total area of each cell in System 1 is 25.3 
square meters, and area of each cell in System 2 is 40.6 square meters. 



Wetland system and 
cell 



Plant species 



Total Percentage of 

coverage total area 
(m2) 



Rank 



System l,Cell 1 








December 1997 


Washingtonii robusta 


3.1 


12.3% 




Typha domingensis 


2.6 


10.4% 




Conocarpus erecta 


2.4 


9.5% 




Nerium oleander 


1.6 


5.9% 




Musa sp. 


1.6 


5.9% 




Alocasia macrorhiza 


0.9 


3.6% 




Pluchea odorata 


0.8 


3.2% 




Sesuvium portulacastrum 


0.8 






Xanthoseum roseum 


0.8 




July 1998 


Conocarpus erecta 


7.0 


28% 




Washingtonii robusta 


6.0 


24% 




Alocasia macrorhiza 


4.8 


19.2% 




Musa sp. 


4.2 


16.8% 




Typha domingensis 


2.8 


11.2% 




Nerium oleander 


2.0 


8% 




Coccoloba uvifera 


1.8 


7.2% 




Xanthosema roseum 


1.3 


5.2% 


System 1, Cell 2 








December 1997 


Washingtonii robusta 


3.3 


13% 




Canna edulis 


2.0 


7.9% 




Hymenocallis littoralis 


1.7 


6.7% 




Musa sp. 


1.6 


6.3% 




Typha domingensis 


1.3 


5.1% 




Oleander nerium 


0.9 


3.6% 




Acrostichum danaefolium 


0.8 


3.2% 




Cyperus ligularis 


0.8 






Chrysobalanus icaco 


0.8 




July 1998 


Washingtonii robusta 


14.4 


57.6% 




Hymenocallis littoralis 


3.9 


15.6% 




Nerium oleander 


2.4 


9.6% 




Ipomoea Pes-caprae 


1.9 


7.6% 




Typha domingensis 


1.4 


5.6% 




Terminalia Catappa 


0.7 


2.6% 




Pedilanthus tithymaloides 


0.6 


2.2% 




Coccoloba uvifera 


0.4 


1.4% 


System 2, Cell 1 








December 1997 


Washingtonii robusta 


5.6 


13.9% 




Musa sp. 


2.4 


5.9% 



1 

2 
3 
4 (tie) 

6 

7 (tie) 



1 
2 
3 
4 
5 
6 
7 
8 

1 
2 
3 
4 
5 
6 
7 (tie) 



1 
2 
3 
4 
5 
6 
7 
8 



2 (tie) 



87 



Wetland system and 


Plant species 


Total 


Percentage of 


Rank 


cell 




coverage 


total area 






Typha domingensis 


(m2) 
2.4 








Alocasia macrorhiza 


1.9 


4.7% 


4 




Nerium oleander 


1.4 


3.5% 


5 (tie) 




Sesuvium portulacastrum 


1.4 








Acalypha hispida 


1.3 


3.2% 


7 




Cissus erosus 


1.2 


2.9% 


8 


July 1998 


Washingtonii robusta 


9.4 


23.2% 


1 




Typha domingensis 


4.4 


10.8% 


2 (tie) 




Nerium oleander 


4.4 


10.8% 






Cissus erosus 


3.6 


8.9% 


4 




Musa sp. 


3.2 


7.9% 


5 




Xanthoseum roseum 


3.0 


7.4% 


6 




Alocasia macrorhiza 


1.3 


3.2% 


7 




Cissus trilofolia 


1.2 


3.0% 


8 


System 2, Cell 2 










December 1997 


Typha domingensis 


3.9 


9.6% 


1 




Alocasia macrorhiza 


2.3 


5.7% 


2 




Canna edulis 


2.1 


5.2% 


3 




Xanthoseum roseum 


1.7 


4.2% 


4 




Musa sp. 


1.6 


3.9% 


5 (tie) 




Washingtonii robusta 


1.6 








Vigna elegans 


1.1 


2.7% 


7 (tie) 




Nerium oleander 


1.1 


0.9 


2.2% 


July 1998 


Nerium oleander 


4.9 


12.1% 


1 




Washingtonii robusta 


4.8 


11.8% 


2 




Typha domingensis 


3.6 


8.9% 


3 




Xanthoseum roseum 


3.5 


8.6% 


4 




Alocasia macrorhiza 


3.1 


7.6% 


5 




Solarium 


2.0 


4.9% 


6 




Schlechtendalii 










Carica Papaya 


1.8 


4.4% 


7 




Acrosiichum danaefolium 


1.7 


4.2% 


8 



88 

System 2 (both around 70%) while Cell 1 of System 1 at 94% cover was still far ahead of 
Cell 2 with 76%. 

Estimates of area covered by dominant species in each wetland treatment cell were 
also done by visual inspection and estimation of cover by each species in May 1997, 
December 1997 and July 1998. These results (Tables 3-7 and Table 3-8) show that 
dominance decreased between May and December 1997. In May 1997, the top 4 species 
covered 38%, 47%, 37% and 37% in individual treatment cells, while in December 1997, the 
top four species covered 32%, 28%, 24% and 21% of the wetlands. For the top 8 species, 
combined coverage in May 1997 was 54%, 56%, 50%, and 49% while in December 1997, 
coverage had fallen to 54%, 49%, 38% and 38%. By July 1998, the top four species in each 
treatment cell had greater canopy cover, (71%, 83%, 45% and 33%). This reflected the 
growth and increased canopy of trees and large palms, such as Washingtonii robusta, 
Conocarpus erecta, and Musa sp. 
Plant frequency 

The frequency of species in the treatment wetlands was evaluated in May 1997, 
December 1997 and July 1998 (Table 3-9). 

The 8 plant species with highest relative frequency in the treatment cells of each 
wetland system in May and December 1 997 are shown in Table 3-9. These results show that 
Carina edulis and Typha domingensis were the two most frequently observed plant species 
overall in May 1997, but that some differences are seen in the wetland cells. In wetland 
System 2, Cell 1, Hymenocallis littoral is is the second most frequent species, and a number 
of different species appear in the top seven species depending on the wetland area. By 
December 1997, the pattern had changed somewhat with Carina edulis coverage 



89 



Table 3-9 Frequency rankings of dominant plants in constructed wetlands in May 1997, 
December 1997 and July 1998 transects. 



Wetland 
location 

System 1 
Cell 1 



Date 



May 
1997 



Most frequent Percent Date Most frequent Percent 

species frequency species frequency 



Carina edulis 
Typha domingensis 



25.4 
12.5 



A I ocas ia macrorhiza 9. 1 

Sesuvium 8.2 
portulacastrum 

Hymenocallis littoral is 5.6 

Solanum erianthum 3.9 

Paspalum virgatum 3.4 

Nerium oleander 2.6 



Dec. Typha 

1997 domingensis 20.3 

Alocasia 11.4 

macrorhiza 

Sesuvium 9.6 

portulacastru 

m 

Hymenocallis 8.0 

littoralis 

Canna edulis 7. 1 

Nerium 3.8 

oleander 

Conocarpus 2.6 

erecta 

Melanthera 2.6 

nivea 



July 
1998 



System 1 May 
Cell 2 1997 



Typha domingensis 

Alocasia macrorhiza 

Hymenocallis 

littoralis 

Canna edulis 

Solanum 

Schlechtendalii 

Scindapsus 

aureus 

Washingtonii robusta 3.6 

Pluchea odorata 3.6 



16.8 

6.4 

5.6 

5.2 
4.8 

4.4 







Dec. 










1997 






Canna edulis 


25.2 




Canna edulis 


17.5 


Hymenocallis littoralis 


14.0 




Typha 
domingensis 


10.8 


Typha domingensis 


8.8 




Hymenocallis 
littoralis 


7.6 


Acrostichum 


4.4 




Acalypha 


7.2 


danaefolium 






hispida 




Sessuvium 


4.4 




Washingtonii 


4.4 


portulastrum 






robusta 




Cyperus ligularis 


3.6 




Melanthera 


4.0 



nivea 



90 



Wetland Date Most frequent 
location species 

Chrysobalanus 
icaco 

Chamaesyce 
hypericifolia 



Percent Date Most frequent Percent 
frequency species frequency 



3.2 
2.4 



Alocasia 


4.0 


macrorhiza 




Cyperus 


4.0 


ligularis 





July 
1998 



System 2 May 
Cell 1 1997 



Hymenocallis 

littoral is 9 2 

Carina edulis 8.4 

Typha domingensis 8.0 

Ipomoea Pes-caprae 8.0 

Washingtonii robusta 6.4 

Alocasia macrorhiza 4.4 

Nerium oleander 4.4 

Phyla nodiflora 4.0 



Typha domingensis 194 

Canna edulis 15.1 

Nerium oleander 5.2 

Ageratum littorale 3.9 

Sessuvium 3.4 

portulastrum 

Phyla nodiflora 3.4 

Ludwigia octavalis 3.0 

Pluchea odorata 3 . 



Dec. 
1997 



Typha 
domingensis 

Canna edulis 

Nerium 
oleander 
Xanthoseum 
roseum 
Sessuvium 
portulastrum 
Ipomoea Pes- 
caprae 
Cissus erosus 
Acalypha 
hispida 
Ageratum 
littorale 



29.7 

12.7 

6.6 

3.4 

3.1 

3.1 

2.2 
2.2 

2.2 



July 
1998 



Wetland Date 



Typha domingensis 


17.6 






Cissus erosus 


8.4 






Alocasia macrorhiza 


6.4 






Nerium oleander 


5.2 






Washingtonii 


4.8 






robusta 








Sesuvium 


2.8 






portulacastrum 








Most frequent 


Percent 


Date 


Most frequent 



Percent 



91 



location 



species 



frequency 



species 



frequency 



System 2 
Cell 2 





Bravaisia tubiflora 


2.4 








Ipomea indica 


2.4 






May 
1997 


Typha domingensis 


21.6 


Dec. Typha 
1997 domingensis 


28.6 




Canna edulis 


19.2 


Canna edulis 


12.1 




Solanum erosanthum 


7.0 


Nerium 
oleander 


7.1 




Eleocharis cellulosa 


6.4 


Alocasia 
macrorhiza 


3.8 




Alocasia macrorhiza 


4.7 


Vigna elegans 


2.9 




Paspalum virgatum 

Hymenocallis 
littoralis 


4.7 
4.1 


Sessuvium 
portulastrum 
Eleocharis 
cellulosa 


2.9 
2.9 




Phyla nodijlora 


4.1 


Hymenocallis 
littoralis 


2.9 




Washingtonii robusta 
Cestrum diurnum 


4.1 
4.1 


Acalypha 
hispida 


2.0 


July 
1998 


Typha domingensis 
Nerium oleander 
Xanthoseum roseum 
Alocasia macrorhiza 
Canna edulis 
Pluchea odorata 
Scindapsus aureus 
Hymenocallis 
littoralis 


20.8 
8.4 
4.8 
4.8 

4.4 
4.4 
4.3 
3.6 








Rhabdadenia biflora 


3.3 







92 

declining (from 17% overall to 12%), Typha domingensis increasing (from 15% 
to 22%) and other cells showing changes in species and their frequency. The cover by vines 
was greater in System 2, with Ipomoea Pes-caprae, Cissus erosus and Vigna elegans among 
the most frequently observed species. By July 1998, the decline ofCanna edulis 
accelerated, both in frequency and in size of individual plants, as it became overtopped by a 
taller canopy. 

Along with greater species richness, System 2 was less heavily dominated by its most 
frequently observed plant species in May 1997. In System 2, Cell 1, the five most frequent 
species constitute 47% of total observations and in System 2, Cell 2, the top five are 52%. By 
contrast in System 1, Cell 1, the top 5 are 60%, and in System 1, Cell 2, are 56% of total 
observations in May 1997. When considered as a whole, in System 1 the top 5 species are 
58.3% of observations, while in System 2, the top 5 are 47.7%. By December 1997, the 
situation had changed, and the two wetlands were more comparable. In System 2's cells 1 
and 2, the top 5 species constituted 56% and 55% of observations, while in wetland System 
1, the top five species represented 60% and 48% of observations. In July 1998, the decrease 
in dominance continued, with the top 5 species constitute 42.4% of observations in System 2, 
and 37.2% in System 1 (Table 3-9). 

Rarely observed species are found in all cells of both systems, but more are found in 
wetland System 2. In May 1997, in System 1, Cell 1, there were 10 species with only 2 
observations and 9 with only 1; in System 1, Cell 2, there were 5 species with only 2 
observations, and 8 with only 1 ; in System 2, Cell 1 , there were 1 1 species with only 2 
observations, and 9 with only 1; and in System 2, Cell 2, there were 12 species with only 2 
observations and also 12 species with only 1 observation. In December 1997, System 1, Cell 



93 



2 



1 had 9 species with 2 observations, 5 species with 1 ; System 1, Cell 2 had 6 species with 2 
observations, 8 species with 1; while System 2, Cell 1 had 13 species with 2 observations, 10 
species with 1; and System 2, Cell 2, had 12 species with 2 observations and 16 with 1. In 
July 1998, System 1 Cell 1 had 4 species with 2 observations and 6 with one; System 1 Cell 
had 4 species with 2 observations and 3 with one. System 2 Cell 1 had 12 species with 2 
observations and 10 with one; System 2 Cell 2 had 5 species with two observations, and 14 
with one. 
Importance values 

Importance values for the plant species in the wetland systems were calculated 
combining their relative frequency (from transect studies) and their relative cover 
(from quadrat analysis) and dividing by two (Brower et al., 1991). Table 3-10 presents the 
Importance Value results which show that in May 1997, Carina edulis and Typha 
domingensis were the two most important plant species overall as they occupied all but one 
of top two rankings in the four treatment cells. In December 1997, Typha remained the 
highest ranking species, but now Washingtonii robusta was second overall. Below that level, 
there was some variability in which plants ranked highest in importance in each treatment 
cell. In July 1998, Typha remained the top species in the two system cells of System 2, but 
Washingtonii robusta and Conocarpus erecta were the top plants in each of System 1 's cells 
(Table 3-10). 

Graphing the rank sequence of species from each system cell is a method of 
comparing dominance vs. evenness of systems (Brower et al, 1991 ). Figure 3-19, Figure 3- 
20, and Figure 3-21 show that there was great similarity in the pattern of 
dominance/evenness for all four of the wetland treatment cells in May 1997, December 



94 



Table 3-10 Importance value ranking of top eight species in each wetland treatment cell, 
May 1997, December 1997 and July 1998 surveys. Values were computed by adding relative 
species frequency and relative species cover and dividing by 2. Maximum value is therefore 
1.0, and total is 1.0 summing all species found in the treatment cell 



Wetland system and cell Survey date Plant species 



Importance 
value 



Rank 



System 1, Cell 1 



System 1, Cell 2 



May 1997 


Canna edulis 


0.31 


1 




Typha domingensis 


0.12 


2 




Sesuvium portulacastrum 


0.10 


3 




Alocasia macrorhiza 


0.09 


4 




Paspalum virgatum 


0.06 


5 




Solarium erianthum 


0.06 


6 




Hymenocallis littoralis 


0.05 


7 




Nerium oleander 


0.04 


8 


Dec. 1997 


Typha domingensis 


0.15 


1 




Alocasia macrorhiza 


0.08 


2 




Washingtonii robusta 


0.08 


3 




Sesuvium portulacastrum 


0.07 


4 




Conocarpus erecta 


0.06 


5 




Nerium oleander 


0.05 


6 




Hymenocallis littoralis 


0.05 


7 




Canna edulis 


0.05 


8 


July 1998 


Conocarpus erecta 


0.13 


1 




Typha domingensis 


0.12 


2 




Washingtonii robusta 


0.10 


3 




Alocasia macrorhiza 


0.10 


4 




Musa sp. 


0.07 


5 




Nerium oleander 


0.06 


6 




Solanum Schlechtendalii 


0.04 


7 




Hymenocallis littoralis 


0.04 


8 


May 1997 


Canna edulis 


0.25 


1 




Hymenocallis littoralis 


0.11 


2 




Melanthera nivea 


0.07 


3 




Sesuvium portulacastrum 


0.06 


4 




Typha domingensis 


0.06 


5 




Acoelorhaphe wrightii 


0.05 


6 




Chrysobalanus icaco 


0.04 


7 




Acrostichum danaefolium 


0.04 


8 


Dec. 1997 


Canna edulis 


0.14 


1 




Washingtonii robusta 


0.11 


2 




Typha domingensis 


0.09 


3 



95 



Wetland system and cell Survey date Plant species Importance Rank 

value 

Hymenocallis littoralis 0.08 4 

Acalypha hispida 0.05 5 

Musa sp. 0.05 6 

Cyperus ligularis 0.04 7 

Acrostichum danaefolium 0.04 8 

July 1998 Washingtonii robusta 0.25 1 

Hymenocallis littoralis 0.11 2 

Ipomoea Pes-caprae 0.07 3 

Typha domingensis 0.06 4 

Nerium oleander 0.06 5 

Canna edulis 0.04 6 

Alocasia macrorhiza 0.03 7 

Solarium Schlechtendalii 0.03 8 

System 2, Cell 1 May 1997 Typha domingensis 0.16 1 

Canna edulis 0.14 2 

Pluchea odorata 0.06 3 

Sesuvium portulacastrum 0.06 4 

Nerium oleander 0.05 5 

Ageratum littorale 0.05 6 

Ipomoea Pes-caprae 0.05 7 

Eleocharis cellulosa 0.04 8 

Dec. 1997 Typha domingensis 0.19 1 

Washingtonii robusta 0.11 2 

Canna edulis 0.08 3 

Nerium oleander 0.06 4 

Mmso sp. 0.05 5 

Sesuvium portulacastrum 0.04 6 

Alocasia macrorhiza 0.04 7 

Acalypha hispida 0.03 8 

July 1998 Typha domingensis 0.14 1 

Washingtonii robusta 0. 14 2 

Cissus erosus 0.09 3 

Nerium oleander 0.08 4 

Musa sp. 0.05 5 

Alocasia macrorhiza 0.05 6 

Xanthoseum roseum 0.05 7 

Hymenocallis littoralis 0.04 8 

System 2, Cell 2 May 1997 Canna edulis 0.24 1 

Typha domingensis 0.19 2 

Nerium oleander 0.08 3 

Sesbania emerus 0.06 4 



96 
Wetland system and cell 



-ell Survey date 


Plant species 


Importance 
value 


Rank 




Alocasia macrorhiza 


0.05 


5 




Eleocharis cellulosa 


0.04 


6 




Paspalum virgatum 


0.04 


7 




Solarium erianthum 


0.04 


8 


Dec. 1997 


Typha domingensis 


0.21 


1 




Carina edulis 


0.10 


2 




Alocasia macrorhiza 


0.06 


3 




Nerium oleander 


0.06 


4 




Vigna elegans 


0.04 


5 




Xanthoseum roseum 


0.03 


6 




Washingtonii robusta 


0.03 


7 




Musa sp. 


0.03 


8 


July 1998 


Typha domingensis 


0.15 


1 




Nerium oleander 


0.10 


2 




Washingtonii robusta 


0.07 


3 




Xanthoseum roseum 


0.07 


4 




Alocasia macrorhiza 


0.06 


5 




Solanum Schlechtendalii 


0.06 


6 




Acrostichum danaefolium 


0.04 


7 




Canna edulis 


0.03 


8 




97 















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100 

1997 and July 1998. Distribution is somewhat more even in December 1997, as evidenced by 
a flatter shape to the graph lines than in the earlier and later measurements. 
Leaf area index 

Data on the structure of vegetation in the wetlands monitored with leaf area index 
(LAI) are summarized in Table 3-11. Photographs of the wetlands illustrating canopy 
development are presented in Figures 3-22 to 3-25. 

The initial development of the canopy in the two wetlands was similar. The overall 
LAI for the System 1 and System 2 wetlands were 4.04 ±0.28 and 3.89 ±0.29 in May 1997. 
However, leaf area indexes were markedly different between the first and second treatment 
cells. The first cells of the two wetland systems averaged 5.56 ± 0.27. By contrast, the second 
cells were substantially lower, averaging 2.33 ± 0.19 (Table 3-11). 

By November 1997, after an additional six months growth, and July 1998, with an 
additional 14 months growth, all cells had increased in LAI. The difference between first and 
second cells had considerably narrowed in System 1 and was no longer evident in System 2. 
Average LAI for System 1 had increased to 5.73 ± 0.48 and System 2 was 6.38 ± 0.51 (Table 
3-11). 
Leaf holes 

Leaf holes due to herbivory and other causes were measured in December 1997 and 
July 1998 (Table 3-12, Table 3-13). 

Overall estimates for the ecosystem were determined by multiplying leaf holes per 
species by species frequency. The result was 4.7% of leaf material in the wetlands in 
December 1997 and 2.1% in July 1998 (Table3-12, Table 3-13). 



101 

Table 3-1 1 Measurements of leaf area index in the treatment cells of the wetland systems, 
May 1997, December 1997 and July 1998. Values are given with standard error of the mean. 

May, 1997 

Wetland Unit No. of observations First Cell Second Cell Overall Wetland 



System 1 93 5.51+/- 0.40 2.54+/- 0.23 4.04+/- 0.28 

System 2 105 5.60+/- 0.36 2.33+/- 0.19 3.89+/- 0.29 



November 1997 

Wetland Unit No. of observations First Cell Second Cell Overall wetland 



System 1 109 6.22+/- 0.4 4.24+/- 0.43 5.23+/- 0.31 

System 2 109 5.76+/- 0.36 4.9+/- 0.31 5.33+/- 0.26 



July 1998 

Wetland Unit No. of observations First Cell Second Cell Overall wetland 

System 1 66 6.68 ±0.46 4.77 ±0.55 5.73+/- 0.48 

System 2 71 6.38 ±0.48 6.39 ±0.54 6.38+/- 0.51 



102 




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105 








Figure 3-25 Photograph of vegetation in wetland system 1, July 1998. 



106 
Table 3-12 Leaf holes in the wetland treatment units, December 1997. 



Name of Species 


Percent Leaf 


Species 




Holes 2 Frequency 11 Contribution 


Carina edulis 


0.15 


0.123 


0.018 


Acalypha hispida 


0.1 


0.036 


0.004 


Hymenocallis littoralis 


0.04 


0.052 


0.002 


Lantana involucrata 


0.16 


0.015 


0.002 


Melanthera nivea 


0.074 


0.029 


0.002 


Solarium Schlechtendalii 


0.11 


0.016 


0.002 


Alocasia macrorhiza 


0.026 


0.047 


0.001 


Cissus erosus 


0.11 


0.006 


0.001 


Cissus sicyoides 


0.26 


0.002 


0.001 


Cyperus ligularis 


0.05 


0.017 


0.001 


Eupatorium albicaule 


0.19 


0.006 


0.001 


Ipomea indica 


0.15 


0.005 


0.001 


Ipomoea Pes-caprae 


0.042 


0.024 


0.001 


Phyla nodiflora 


0.15 


0.005 


0.001 


Sesuvium portulacastrum 


0.014 


0.046 


0.001 


Terminalia Catappa 


0.058 


0.009 


0.001 


Vigna elegans 


0.1 


0.013 


0.001 


Washingtonii robusta 


0.03 


0.022 


0.001 


Acrostichum danaefolium 


0.014 


0.014 


0.000 


Ageratum littorale 


0.04 


0.008 


0.000 


Anthurium schlechtendallii 


0.012 


0.005 


0.000 


Anthurium sp. 


0.03 


0.005 


0.000 


Asclepias curossavica 


0.01 


0.001 


0.000 


Bidens pilosa 


0.018 


0.003 


0.000 


Bravaisia tubiflora 


0.07 


0.005 


0.000 


Caesalpinia pulcherrima 


0.014 


0.003 


0.000 


Caladium bicolor 


0.02 


0.007 


0.000 


Carica Papaya 


0.05 


0.001 


0.000 


Chamaedorea Seifrizii 


0.012 


0.001 


0.000 


Chamaesyce hypericifolia 


0.038 


0.004 


0.000 


Chrysobalonus icaco 


0.002 


0.013 


0.000 


Citrus aurianthum 


0.014 


0.001 


0.000 


Coccoloba uvifera 


0.048 


0.008 


0.000 


Conocarpus erecta 


0.02 


0.007 


0.000 


Corchorus siliquosus 


0.07 


0.005 


0.000 



107 



Name of Species 


Percent Leaf 


Species 




Holes 3 Frequency 11 Contribution 


Desmodium incanum 


0.12 


0.002 


0.000 


Distichlis spicata 





0.006 


0.000 


Eleocharis cellulosa 


0.01 


0.006 


0.000 


Flaveria linearis 


0.05 


0.004 


0.000 


Iresine celosioides 


0.03 


0.002 


0.000 


Ixora coccinea 





0.007 


0.000 


Kalanchoe pinnata 


0.008 


0.003 


0.000 


Lochnera rosea 


0.09 


0.001 


0.000 


Malvaviscus arboreus 


0.022 


0.003 


0.000 


Nerium oleander 





0.052 


0.000 


Nopalea cochinillifera 


0.008 


0.001 


0.000 


Paspalum virgatum 


0.014 


0.018 


0.000 


Pedilanthus tithymaloides 


0.03 


0.011 


0.000 


Pelliciera alliacea 


0.09 


0.002 


0.000 


Philodendron sp 


0.004 


0.001 


0.000 


Pluchea odorata 


0.046 


0.009 


0.000 


Psychotria nervosa 


0.02 


0.001 


0.000 


Rabdadenia biflora 


0.08 


0.003 


0.000 


Rhoeo discolor 


0.02 


0.009 


0.000 


Sansevieria triasiate 


0.01 


0.010 


0.000 


Scindapsus aureus 


0.03 


0.008 


0.000 


Selenicereus dontielarii 





0.001 


0.000 


Senna biflora 


0.004 


0.001 


0.000 


Syngonium sp. 


0.07 


0.002 


0.000 


Thrinax radiata 





0.004 


0.000 


Typha domingensis 


0.002 


0.220 


0.000 


Vigna luteola 


0.07 


0.001 


0.000 


Viguiera dentata 


0.06 


0.001 


0.000 


Wedelia trilobata 


0.1 


0.001 


0.000 


Xanthosoma roseum 


0.014 


0.026 


0.000 


Zamia purpuraceus 





0.005 


0.000 


Zephranthes Lindleyana 


0.014 


0.005 


0.000 


Total 




1.000 


0.047 



Portion of measured leaves of one species which showed holes 
Frequency is based on the frequency of the species in the wetlands 
Product of percent holes and species frequency. 



108 
Table 3-13 Leaf holes in the wetland treatment units, July 1998 data. 



Name of Species Percent Leaf Species 

Holes 3 Frequency 15 Contribution 



Solatium Schlechtendalii 
Alocasia macrorhiza 
Nerium oleander 
Sesuvium portulacastrum 
Bidens pilosa 
Carina edulis 
Hymenocallis littoralis 
Phyla nodiflora 
Pluchea odorata 
Scindapsus aureus 
Typha domingensis 
Xanthosoma roseum 
Acrostichum danaefolium 
Ageratum littorale 
Aloe vera 

Alternanthera ramossissima 
Anthurium schlechtendallii 
Anthurium sp. 
Bravaisia tubiflora 
Caesalpinia pulcherrima 
Caladium bicolor 
Capraria biflora 
Car tea Papaya 
Chamaedorea Seifrizii 
Chamaesyce hypericifolia 
Chrysobalonus icaco 
Cissus erosus 
Cissus sicyoides 
Citrus aurianthum 
Coccoloba uvifera 
Conocarpus erecta 
Corchorus siliquosus 
Cordia sebestena 
Crinum amabile 
Desmodium tortuosum 
Distichlis spicata 



0.11 


0.038 


0.004 


0.028 


0.055 


0.002 


0.028 


0.060 


0.002 


0.054 


0.030 


0.002 


0.06 


0.012 


0.001 


0.022 


0.055 


0.001 


0.01 


0.062 


0.001 


0.06 


0.017 


0.001 


0.034 


0.028 


0.001 


0.018 


0.036 


0.001 


0.004 


0.158 


0.001 


0.05 


0.028 


0.001 


0.02 


0.018 


0.000 


0.04 


0.010 


0.000 


0.028 


0.003 


0.000 


0.014 


0.002 


0.000 


0.014 


0.006 


0.000 


0.018 


0.003 


0.000 


0.014 


0.023 


0.000 





0.001 


0.000 





0.007 


0.000 


0.04 


0.003 


0.000 


0.024 


0.001 


0.000 


0.002 


0.002 


0.000 





0.007 


0.000 


0.01 


0.006 


0.000 





0.029 


0.000 


0.004 


0.006 


0.000 


0.004 


0.003 


0.000 


0.034 


0.013 


0.000 


0.018 


0.020 


0.000 


0.05 


0.004 


0.000 


0.004 


0.001 


0.000 


0.004 


0.002 


0.000 


0.014 


0.006 


0.000 





0.005 


0.000 



109 



Name of Species 


Percent Leaf Species 




Holes" Frequency b Contribution 


Eupatorium albicaule 


0.018 


0.007 


0.000 


Flaveria linearis 





0.001 


0.000 


Ipomea indica 


0.004 


0.006 


0.000 


Ipomoea Pes-caprae 


0.014 


0.033 


0.000 


Ixora coccinea 


0.034 


0.009 


0.000 


Kalanchoe pinnata 


0.04 


0.002 


0.000 


Leucaena glauca 





0.002 


0.000 


Mimosa sp. 


0.01 


0.003 


0.000 


Malvaviscus arboreus 





0.004 


0.000 


Musa sp. 


0.004 


0.015 


0.000 


Nopalea cochinillifera 


0.03 


0.001 


0.000 


Paspalum virgatum 


0.02 


0.003 


0.000 


Pedilanthus tithymaloides 


0.004 


0.014 


0.000 


Philodendron sp. 


0.025 


0.001 


0.000 


Phylanthus niruri 


0.03 


0.001 


0.000 


Psychotria nervosa 


0.014 


0.003 


0.000 


Rabdadenia biflora 





0.008 


0.000 


Rhizophora mangle 





0.003 


0.000 


Rhoeo discolor 


0.01 


0.017 


0.000 


Sansevieria triasiate 


0.008 


0.009 


0.000 


Senna biflora 


0.004 


0.003 


0.000 


Terminalia Catappa 


0.004 


0.017 


0.000 


Thrinax radiata 


0.07 


0.006 


0.000 


Vigna luteola 





0.003 


0.000 


Washingtonii robusta 


0.004 


0.044 


0.000 


Wedelia trilobata 


0.004 


0.008 


0.000 


Zamia purpuraceus 





0.004 


0.000 


Zephranthes Lindleyana 


0.05 


0.007 


0.000 



Total 1.00 0.021 



b 



Portion of measured leaves of one species which showed holes 
Frequency is based on the frequency of the species in the wetlands 
Product of percent holes and species frequency. 



110 

More holes were found in Cissus sicyoides (26%), Eupatorium albicaule (19%), 
Lantana involucrata (16%), Canna edulis (15%), Ipomea indica (15%), Phyla nodiflora 
(15%), Solarium schlectendalionum (1 1%) and Cissus erosus (1 1%). Because of its 
abundance Canna edulis (1.8%) was responsible for over one-third of the total. Eighteen 
species accounted for 89% of total herbivory in the wetlands in December 1997 (Table 3-12). 

By July 1998, when average leaf holes were 1.8%, the leading species were Thrinax 
radiata (7%), Bidens pilosa (6%), Phyla nodiflora (6%), Sesuvium portulacastrum (5.4%), 
Xanthoseum roseum (5%) and Cor chorus siliquosus (5%). Leaf holes were more evenly 
divided among species than in December 1997, with Solanum Schlechtendalii contributing 
the highest individual amount (4%), while Alocasia macrorhiza, Sesuvium portulacastrum, 
and Nerium oleander each contributed 2% (Table 3-13). 
Surface organic matter 

Results of analysis of organic matter on the gravel surface of treatment systems are 
presented in Figure 3-26. 

Average organic matter surface material was initially 1582 ± 242 g m~ 2 (dry weight). 
In July, 1998, after twenty three months of wetland operation since planting, surface organic 
matter averaged 1458 ± 254 g m 2 in System 1 Cell 1, 1515 ± 373 g m" 2 in System 1 Cell 2, 
1210 ±81 g m" 2 in System 2 Cell 1, and 1610 ± 242 g m 2 in System 2 Cell 2. The overlap of 
the standard error bars shows that these values are not statistically different from the starting 
value. T-tests for samples of unequal variance show their probabilities to be p<0.73, p<0.96, 
p<0.36 and p<0.20 respectively indicating that statistically there was no significant change. 



Ill 







Figure 3-26 Surface organic matter in the wetland treatment cells. Data presented are 
those of initial mulching (August 1996) and surface organic matter (July 1998), after 
23 months of operation. Bars are ± standard errors. 



112 

Solar insolation 

Data on solar insolation and canopy interception in the wetland systems are presented 
in Table 3-14. Part of the canopy of wetland System 2 in July 1998 is shown in Figure 3 -27. 

On a summer, cloudless day, near mid-day when outside ambient solar insolation 
levels averaged 7464 ± 25 u.moles m" 2 , solar insolation reaching ground level in the wetland 
systems averaged 373 ± 20 ujnoles m" 2 in System 1 Cell 1, 367 ± 32 umoles m" 2 in System 1 
Cell 2, 563 ± 51 umoles m" 2 in System 2, Cell 1, and 504 ± 61 ujnoles m" 2 in System 2, Cell 2 
(Table 3-14). These data represent canopy interception reductions of 95% in System 1 Cell 1, 
93% in System 1 Cell 2, 82% in System 2 Cell 1 and 90% in System 2 Cell 2. 

Measurements of solar insolation reaching the perimeters of the wetland treatment 
cells (the outer 0.5 m), show that in System 1 Cells 1 and 2, the light levels are slightly lower 
than but comparable to average light levels for the whole treatment cell (4.9% on the 
perimeter vs. 5% for Cell 1, and 6.8% on the perimeter vs. 7.5% for Cell 2). 
Perimeter light levels are considerably higher, however, for wetland System 2, with Cell 1 
perimeter light averaging 33% of ambient vs. 18. 1% for the whole cell, and in Cell 2 
perimeter light averaging 12.1% of ambient compared to 9.8% for the whole cell. The 
statistical significance of these differences (by t-test for two samples of unequal variance) 
are p<0. 12 for System 2 Cell 1 and p<0. 19 for System 2 Cell 2. 
Canopy closure 

Canopy closure of the wetland treatment cells was analyzed with hemispheric canopy 
photographs 23 months after planting (Table 3-15, Figure 3 -28). 



113 



Table 3-14 Insolation levels and their reduction in the constructed wetlands, 28 July 1998 
between 1050 and 1 145 AM. Perimeter light levels are the measured insolation at locations 
0.5 m inside the wetland systems along their outside edges. 



Location 


Solar insolation 


Percent of 




u.mol 


ambient light 


Amhipnt 


7464 ± 25 
373 ± 20 




./IJllL/lVUl. 

System 1 Cell 1 


5.0% 


System 1 Cell 1 


367 ± 32 


4.9% 


Perimeter 






System 1 Cell 2 


563151 


7.5% 


System 1 Cell 2 


504 ±61 


6.8% 


Perimeter 






System 2 Cell 1 


1350 ±225 


18.1% 


System 2 Cell 1 


2460 ±641 


33.0% 


Perimeter 






System 2 Cell 2 


722 ± 64 


9.8% 


System 2 Cell 2 


902 ±112 


12.1% 


Perimeter 







114 




115 



Table 3-15 Light penetration and canopy closure in the wetland systems and adjoining 
mangrove wetland, 29 July 1998. Data presented ± standard error of the mean. 



Location 


Number of 
Photographs 


Light through 

canopy 

(percent) 


Canopy closure 
(percent) 


System 1 Cell 1 


9 


12.5 ±1.4 


87.5 ±1.4 


System 1 Cell 2 


9 


16.1 ±2.9 


83.9 ±2.9 


System 2 Cell 1 


9 


15.2 ±2.6 


84.8 ±2.6 


System 2 Cell 2 


8 


13.1 ±1.8 


86.9 ±1.8 


Mangrove wetland 


9 


14.8 ±1.8 


85.2 ±1.8 



116 




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Canopy closures were greater than 80% in all the treatment cells. The largest closure 
in System 1 Celll (87.5 ± 1.4%) was slightly greater than in the least, System 1 Cell 2 (83.9 
± 2.9%). The significance of this difference by t-test for two samples of unequal variance is 
p<0.27. Canopy closures in System 1 (85.7%), System 2 (85.8%) and the mangrove receiving 
wetland in the vicinity of the discharge (85.2 ± 1.8%) were similar. 
Chemical Characteristics and Uptake 

Phosphorus 

Data on total phosphorus from the two wetland systems are presented in Figure 3-29 
and Figure 3-30. The influent concentrations and reduction of phosphorus in the wastewater 
varied seasonally in both systems, as they did for all other wastewater constituents as a result 
of large seasonal changes in numbers of residents and tourists in the buildings connected to 
the wetland units. System 1 had average discharge of 1.1 ± 0.2 mg/liter phosphorus, 
compared to the background levels in the cenote of 0.46 ± 0.17 mg/liter (Table 3-16). In 
wetland System 2 discharge water contained 2.7 ± 0.4 mg/liter P. Overall reduction in 
phosphorous between initial levels in the septic tank and discharge from wetland Cell 2 was 
greater in System 1 which averaged 84% while System 2 had a P reduction of 71% on 
average (Table 3-17) 

Tests to determine the variability in analysis of total P at the University of Florida 
Water Reclamation Laboratory were conducted with the samples of 31 August 1997 and 27 
September 1997. Results in Table 3-18 show that the largest standard error of the mean was 
less than 6% of the determination. 









118 









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120 



Table 3-16 Total phosphorus content of water samples from cenote (groundwater well) near 
wetland treatment systems. 



Date 


Total phosphorus 
mg/liter 


28 Jan 97 


0.52 


28 Feb 97 


0.37 


31 Mar 97 


0.33 


30 Apr 97 


0.17 


8 Jul 97 


0.75 


11 Aug 97 


0.5 


31 Aug 97 


0.35 


27 Sep 97 


0.9 


27 Oct 97 


0.4 


1 Dec 97 


0.3 


Mean ± standard 


0.46 ± 0.07 


error 









i 



121 



Table 3-17 Total phosphorus in effluent from septic tank and discharge effluent from 
wetland treatment systems and percent reduction of phosphorus levels. 



Date of 


System 1 


Discharge 


Percent 


System 2 


Discharge 


Percent 


Test 


Septic 


from 


Reduction 


Septic 


from 


Reduction 




tank 


System 1 




tank 


System 2 






mg P/liter 


mg P/liter 




mg P/liter 


mg P/liter 




28 Jan 97 


6.0 


0.4 


93.7 


7.3 


0.28 


96.1 


28 Feb 97 


12.2 


N/A 




10.3 


4 


61.0 


31 Mar 97 


14.8 


1.4 


90.5 


6.1 


3.75 


38.5 


30 Apr 97 


14.3 


0.8 


94.4 


4.0 


0.95 


76.3 


8 Jul 97 


5.8 


0.6 


89.6 


4.7 


0.55 


88.3 


11 Aug 97 


4.8 


0.55 


88.5 


2.3 


1.55 


32.6 


31 Aug 97 


3.3 


0.55 


83.3 


0.4 


0.55 


-37.5 


27 Sep 97 


1.4 


0.65 


53.6 


1.4 


0.45 


66.7 


27 Oct 97 


2.1 


0.55 


73.8 


1.4 


0.85 


37.0 


1 Dec 97 


6.4 


2.3 


64.1 


6.4 


1.3 


79.7 


3 Mar 98 


8.55 


0.54 


93.7 


10.75 


4.77 


55.6 


30 Mar 98 


5.45 


1.07 


80.4 


8.84 


4.05 


54.2 


30 Apr 98 


9.93 


0.52 


94.8 


17.43 


4.07 


76.6 


31 May 98 


5.64 


1.67 


70.4 


16.59 


5.96 


64.1 


30 June 98 


3.93 


1.91 


51.4 


27.59 


4.72 


82.9 


22 Jul 98 


4.22 


2.2 


47.9 


23.39 


5.1 


78.2 


19 Aug 98 


5.95 


1.52 


74.5 


13.71 


3.71 


72.9 


Mean± 


7.0 ±1.0 


1.1 ±0.2 




9.1 ±1.7 


2.7 ±0.4 




standard 














error 














Overall 
reduction 






83.9 






70.9 



122 



Table 3-18 Total phosphorus content of water samples from the treatment wetlands. 



Wetland treatment area 



Date of sample 



Wetland System 1, septic tank 31 August 1997 

Cell 1 31 August 1997 

Cell 2 31 August 1997 

Wetland System 2, septic tank 31 August 1997 

Cell 1 31 August 1997 

Cell 2 31 August 1997 



Average result from Standard error of 
3 tests the mean 

mg P/liter mg P/liter 



3.38 
1.35 
0.58 
0.42 
0.58 
0.53 



± 0.044 

±0.05 

±0.017 

±0.017 

± 0.033 

±0.017 



Wetland System 1, septic tank 27 September 1997 1.47 

Cell 1 27 September 1997 1.72 

Cell 2 27 September 1997 0.6 

Wetland System 2, septic tank 27 September 1997 1 .42 

Cell 1 27 September 1997 0.62 

Cell 2 27 September 1997 0.45 



± 0.033 
±0.017 
±0.029 
± 0.033 
± 0.033 




123 

Nitrogen 

Figures 3-31 and 3-32 present results of total nitrogen water quality tests from the 
wetland systems. Final effluent reduction of initial nitrogen tended to become more efficient 
as the wetland systems developed. In the more heavily nutrient-loaded wetland System 2, 
which had final effluent N concentrations in the septic tank ranging from 38 mg N/liter (28 
February 1997 to 6 mg N/liter (30 April 1997, 8 July 97 and 1 1 August 1997) to 1-2 mg/liter 
(31 August 1997 and 29 September 1997). There was considerable variability, septic tank N 
concentrations ranging from a high of 1 17 mg N/liter to a low of 6 mg N/liter (Table 3-19). 

Ammonia (NH 3 ) analysis was conducted, when the plants were still very 

undeveloped, on 12 January 1997 (Table 3-19). Wetland System 1 had only a 30% reduction 
(from 17.2 mg N/liter in the septic tank to 12 mg N/liter in discharge water from Cell 2). 
Wetland System 2 had a 46% reduction (from 32 mg N/liter in the septic tank to 17.2 mg 
N/liter in wetland Cell 2). The rest of the nitrogen analyses were for total N. 

The nearby cenote had an average concentration of 7.6 ± 1.8 mg N/liter from 
laboratory analyses conducted concurrently with those for the constructed wetlands (Table 3- 
20). Discharge water from Wetland System 1 had an average N concentration of 6. 1 ± 1. 1 mg 
N/liter, statistically not significantly different than the cenote. Discharge water from Wetland 
System 2 averaged 13.9 ± 3.5 mg N/liter. 

During the course of the study, total nitrogen levels in the wetland system discharge 
effluent were reduced from initial septic tank levels by an average of 86.0% in wetland 
System 1 and 73.1% in wetland System 2 (Table 3-19). 



124 



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126 



Table 3-19 Total nitrogen in effluent from septic tank and discharge effluent from wetland 
treatment systems and percent reduction of nitrogen levels. 



Date of 


System 1 


Discharge 


Percent 


System 2 


Discharge 


Percent 


Test 


Septic 


from 


Reduction 


Septic 


from 


Reduction 




tank 


System 1 




tank 


System 2 






mg N/liter 


mg N/liter 




mg N/liter 


mg 














N/liter 




28 Jan 97 


17.2 


12 


30.2 


32 


17.2 


46 3 


28 Feb 97 


108 


N/A 




72 


38 


47.2 


31 Mar 97 


132 


4 


97.0 


36 


26 


27.8 


30 Apr 97 


132 


10 


92.4 


36 


6 


83.3 


8 Jul 97 


48 


8 


83.3 


36 


6 


83.3 


1 1 Aug 97 


36 


6 


83.3 


16 


6 


62.5 


31 Aug 97 


10 


2 


80.0 


6 


1 


83.3 


27 Sep 97 


20 


6 


70.0 


8 


2 


75.0 


27 Oct 97 


22 


8 


63.6 


10 


2 


80.0 


1 Dec 97 


38 


14 


63.2 


72 


14 


80.6 


3 Mar 98 


7.6 


3.82 


49.7 


58.4 


4.86 


91.7 


30 Mar 98 


8.44 


5.51 


34.7 


94.45 


12.5 


86.8 


30 Apr 98 


16.99 


0.7 


95.9 


87.8 


4.82 


94.5 


31 May 98 


53.36 


10.74 


79.8. 


20.38 


10.64 


47.8 


30 Jun 98 


25.88 


0.28 


98.9 


53.96 


19.1 


64.6 


22 Jul 98 


47.22 


0.86 


98.2 


117.5 


9.32 


92.1 


19 Aug 98 


22.34 


12.48 


44.1 


59.6 


16.2 


72.8 


Mean +/- 


43.819.9 


6.1 ±1.1 




51.5±9.0 


13.9 ±3.5 




standard 














error 














Overall 






86.0 






73.1 


reduction 
























127 



Table 3-20 Total nitrogen content of water samples from cenote (groundwater well) near 
wetland treatment systems. 



Date 


Total nitrogen 
mg N/liter 


28 Jan 97 


19.6 




28 Feb 97 


10 




31 Mar 97 


8 




30 Apr 97 


4 




8 Jul 97 


8 




1 1 Aug 97 


10 




31 Aug 97 


1 




27 Sep 97 


4 




27 Oct 97 
1 Dec 97 


10 

1 

1 




Mean ± standard error 


7.6 ± 


1.8 



128 

Biochemical oxygen demand 

BOD-5 (biochemical oxygen demand, 5 day test) analyses are presented in Figure 3- 
33 and Figure 3-34. Reduction of BOD improved after the initial analyses in January 1997 
shortly after the wetlands were first connected to sewage inputs 

Table 3-21 presents septic tank effluent and final discharge levels of BOD from the 
wetlands. Wetland System 1 had average discharge concentration of 12.4 ± 1.7 mg BOD/liter 
over the course of study. Wetland System 2 had an average discharge of 23.4 ± 6.6 mg 
BOD/liter. 

Wetland System 2, which received sewage from a higher percentage of its design 
population, showed higher levels of influent BOD, with septic tank analyses averaging 161.7 
mg/1 compared to 129 mg/1 in System l's septic tank effluent (Table 3-21). BOD reduction 
was comparable in the two wetlands, with wetland System 1 averaging a 87.7% reduction 
compared to 83.5% in wetland System 2. 

Final effluent BOD from the wetland System 1 was around 40% lower than the 
nearby cenote whose BOD averaged 20.7 +/- 3.9 mg/liter (Table 3-22), while discharge 
effluent from wetland System 2 was about 1 5% higher. 
Total suspended solids 

Results of total suspended solids (TSS) analyses in effluents from septic tanks and 
treatment systems are presented in Table 3-23 and Table 3-24 and in Figure 3-35 and Figure 
3-36. 

During the study, TSS averaged around 70 mg/liter in the two septic tanks' effluent 
and was reduced 41% on average. Suspended solids were consistently higher in wetland 






129 



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131 



Table 3-21 Biochemical oxygen demand (BOD-5) in effluent from septic tank and discharge 
effluent from wetland treatment systems and percent reduction. 



Date of System 1 Discharge Percent System 2 Discharge Percent 

Test Septic from Reduction Septic from Reduction 

tank System 1 tank System 2 

mg BOD/1 mg BOD/1 mg BOD/1 mg BOD/1 



12 Jan 97 


48.3 


12.6 


73.9 


108.3 


53.4 


50.7 


22 Jan 97 


120 


15 


87.5 


240 


35.0 


85.4 


2 Feb 97 


59.1 


14.7 


75.1 


111 


18.9 


83.0 


3 Apr 97 


120 


5 


95.8 


100 


20.0 


80.0 


2 Jul 97 


300 


16 


94.7 


263 


14.0 


94.7 


29 Sep 97 


112 


9 


92.0 


150 


6.0 


96.0 


1 Dec 97 


96 


16 


83.3 


112 


12.0 


89.3 


20 Mar 


186 


21 


88.7 


171 


29 


83.0 


98 














17Jun98 


120 


2 


98.3 


161.7 


23.4 


83.5 


Mean± 


129 


12.4 




161.7 


22.8 




standard 


± 34.1 


± 1.7 




± 27.8 


± 6.6 




error 














Overall 






87.7 






83.5 


reduction 

































132 



Table 3-22 Biochemical oxygen demand (BOD-5) content of water samples from cenote 
(groundwater well) near wetland treatment systems. 



Date BOD-5 

mg BOD/liter 



12 Jan 97 


29.7 


28 Jan 97 


15.0 


2 Feb 97 


16.0 


3 Apr 97 


25.0 


2 Jul 97 


32.0 


29 Sep 97 


6.5 


1 Dec 97 


12.0 


Mean± standard error 


20.7 ± 3.9 



133 



Table 3-23 Total suspended solids (TSS) concentrations and reduction in septic tank and 
discharge water from the Akumal wetland treatment systems. 



Date of 


System 1 


Discharge 


Percent 


System 2 


Discharge 


Percent 


Test 


Septic 


from 


Reductio 


Septic tank 


from 


Reduction 




tank 


System 1 


n 


mg TSS/1 


System 2 


(Increase) 




mg TSS/1 


mg TSS/1 


(Increase) 


. 


mg TSS/1 




12 Jan 97 


17.2 


12.0 


30 


32 


17.4 


46 


28 Feb 97 


57.6 


29.2 


49 


59.2 


33.2 


44 


31 Mar 97 


46 


27.2 


41 


45.2 


36.8 


19 


30 Apr 97 


56 


41.6 


26 


34.4 


27.2 


21 


8 Jul 97 


31 


18 


42 


37 


9 


76 


1 1 Aug 97 


42.5 


22.5 


47 


33.5 


25.5 


24 


27 Sep 97 


8 


16 


(+100) 


23.2 


16 


31 


29 Oct 97 


2 


32.8 


(+1540) 


37.6 


35.6 


5 


3 Jan 98 


31.6 


20 


37 


53.2 


16 


70 


24 Jan 98 


40 


16.8 


58 


48 


27.2 


43 


3 Mar 98 


100 


56 


44 


77 


64 


17 


30 Mar 98 


80 


55 


31 


85 


48 


44 


30 Apr 98 


79 


65 


18 


106 


97 


8 


31 May 98 


64 


79 


(+23) 


227 


66 


71 


30 Jun 98 


65 


58 


11 


238 


60 


75 


22 Jul 98 


62 


76 


(+23) 


209 


67 


68 


19 Aug 98 


131 


23 


82 


118 


26 


78 


Mean± 


53.7 ± 


38.2 ± 5.4 




86.1 ±17.3 


39.5 ±5.8 




standard 


8.0 












error 














Overall 






29.0 






54.1 


reduction 















134 



Table 3-24 Total suspended solids (TSS) content of water samples from cenote 
(groundwater well) near wetland treatment systems. 



Date 


Total suspended solids 
mg TSS/liter 


12 Jan 97 


19.6 


28 Feb 97 


20.4 


31 Mar 97 


34.4 


30 Apr 97 


24.4 


8 Jul 97 


20 


11 Aug 97 


26.5 


27 Sep 97 


28.4 


29 Oct 97 


10.4 


Mean ± standard error 


23.0 ±2.5 



135 



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137 

System 2 and were reduced more (54%) than in System 1 (29% reduction). On average both 
systems reduced TSS to around 39 mg/liter but discharge varied from under 20 mg/1 to over 
90 mg/1 (Table 3-23). TSS in the nearby cenote averaged 23.0 ± 2.5 mg/liter (Table 3-24). 
TSS reduction varied widely, both on a percentage basis, and in concentrations in 
effluent water. For example, several times wetland System 1 showed higher discharge TSS 
than influent TSS, and suspended solid concentrations were higher during March - August 
1998 than they had been earlier in the study (Table 3-23). This may reflect release of 
materials from biota or gravel of the wetlands themselves. 
Alkalinity 

Data on alkalinity is presented in Table 3-25. Alkalinity in the septic tanks 
was far lower (155 mg/1) than in either wetland System 1 or wetland System 2. These 
systems averaged 308 mg/1 and 344 mg/1 alkalinity respectively. Alkalinity in the cenote 
was lower than in the wetlands, averaging 252 mg/1. 
Salinity 

Salinity observations are presented in Table 3-26. Salinity decreased 
as the sewage effluent passed from septic tank through Celll and Cell 2 of the 
wetland systems. Average salinity was 4. 1 ± 0.2 ppt (parts per thousand salt) in System 1 
septic tank but decreased to 3.3 ± 0.3 ppt salt in Cell 2 effluent. In System 2 variability was 
greater, and salinity differences were not statistically significant. In System 2 septic tank 
effluent averaged 3.6 ± 0.2 ppt salt, while in Cell 2 it was 2.6 ± 0.8. Salinity in the cenote 
averaged 2.6 ± 0.2 ppt. 



138 
Table 3-25 Alkalinity in septic tanks, wetland systems and cenote. 



Location 27 Sep 97 29 Oct 97 Average 



Septic tank System 1 72 32 52 

Wetland 1 Cell 1 248 414 331 

Wetland 1 Cell 2 266 304 285 

Septic tank System 2 214 300 257 

Wetland 2 Cell 1 320 344 332 

Wetland 2 Cell 2 360 350 355 

Cenote 224 280 252 






139 



Table 3-26 Salinity in septic tanks, wetland system and cenote. Salinity expressed as parts 
per thousand salt (ppt). 



Date System 1 Celll Cell 2 System 2 Cell 1 Cell 2 Cenote 

Septic tank ppt ppt Septic tank Ppt ppt Ppt 

ppt ppt 



12 Jan 97 


3.5 


2.5 


2.5 


4 


3 


2 


2 


2 Feb 97 


4.5 


4 


3 


3 


1 


0.5 


2 


28 Feb 97 


4 


4 


4 


4 


5 


5 


3 


14 Apr 97 


4 


3.5 


3.5 


3 


2 


2 


3 


21 Dec 97 


4.5 


4 


3.5 


4 


3 


3.5 


3 


Mean± 


4.1 


3.6 


3.3 


3.6 


2.8 


2.6 


2.6 


std. error 


±0.2 


±0.3 


±0.3 


±0.2 


±0.7 


±0.8 


±0.2 



140 
Reduction in Coliform Bacteria 

Figure 3-37 and Figure 3-38 are graphs of coliform bacteria concentrations in the 
septic tanks and treatment cells of the wetlands. These data show levels of the bacteria were 
reduced by 99.87% on average after treatment in the wetlands (Table 3-27). 

Final effluent coliform bacteria levels were fairly uniform for the two wetland 
systems, averaging 1580 ± 810 colonies (MPN)/100 ml in wetland System 1 and 2850 ± 
1 160 (MPNyiOO ml in wetland System 2 (Table 3-27). 

Consistent reduction of fecal coliform bacteria was achieved as the wetlands 
developed, although the absolute numbers varied widely between tests. Even initial tests in 
January 1997 showed 99% reduction (wetland System 1) and 99.8% reduction (wetland 
System 2). Subsequent tests generally showed reductions of 99.9+% in both wetlands (Table 
3-27). 

Concentrations of coliform bacteria in the final discharge into the mangroves, 
although numerically lower, were not statistically significant from coliform bacteria 
concentrations in the cenote, which averaged 3,339 ± 2,267 (Table 3-28). 
Phosphorus Uptake by Limestone 

Ca/Mg analysis of limestone 

Table 3-29 presents results of analysis of the Yucatan limestone gravel used in the 
wetland treatment units for calcium and magnesium content. Calcium constitutes 26.6 ± 0.6 
percent of the gravel material and magnesium is 1 1.9 ± 0.2 percent by weight. If both occur 
primarily as carbonate minerals (e.g. calcite, Mg-calcite, aragonite, and dolomite), we can 
calculate their overall molecular weight as 100.1 for CaC03 and 84.3 for MgC0 3 . Thus, 



141 



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143 



Table 3-27 Coliform bacteria concentrations in effluent from septic tank and discharge 
effluent from wetland treatment systems and percent reduction. Data is in units of most 
probable number of colonies per 100 ml (MPN/100 ml). 



Date of System 1 Discharge Percent System 2 Discharge Percent 

Test Septic from Reduction Septic tank from Reduction 

tank System 1 MPN/100 System 2 

MPN/100 MPN/100 ml MPN/100 

ml ml ml 



27 Jan 97 


8,000 


80 


99.0 


1,300 


2 


99.85 


3 Apr 97 


160,000 


2 


99.99 


17,000 


2 


99.99 


8 July 97 


4,400,000 


4,100 


99.91 


5,000,000 


4,000 


99.92 


29 Sep 97 


8,000,000 


1,280 


99.98 


12,000,000 


1,100 


99.99 


1 Dec 97 


4,000,000 


3,000 


99.93 


8,000,000 


4,000 


99.95 


20 Mar 98 


6,200,000 


520 


99.97 


8,600,000 


2,180 


99.97 


23 June 98 


1,200,000 


2,100 


99.82 


11,200,000 


8,700 


99.92 


Mean +/- 

standard 

error 


3,424,000 

± 

1,167,000 


1,580 
±590 




6,403,000 

± 

1,861,000 


2,850 
±1,160 




Overall % 
reduction 






99.80 






99.94 



144 



Table 3-28 Coliform bacteria concentrations in water samples from cenote (groundwater 
well) near wetland treatment systems. Data is in units of MPN/100 ml (most probable 
number of colonies per 100 ml). 



Date 


Coliform bacteria 




MPN/100 ml 


27 Jan 97 


1,100 


3 Apr 97 


1,100 


8 July 97 


1014 


29 Sep 97 


10.140 


Mean +/- standard error 


3,339 ± 2,267 






145 



Table 3-29 Calcium/magnesium content of Yucatan limestone gravel as analyzed by 
inductive coupled plasma spectroscopy. 



Sample Percent calcium Percent magnesium 

1 25.6 12.5 

2 26.3 12.1 

3 28.2 11.7 

4 25.4 12.1 

5 27.7 11.2 
Average ± standard error of the 26.64 ± 0.56 1 1 .92 ± 0.22 

mean 






146 

carbonate minerals constitute over 95% of the material. This compares with published 
estimates, for example, of Pleistocene dune rocks of northeastern Quintana Roo being totally 
carbonate, dominated by aragonite with 20-40% mg-calcite and small amounts of calcite, and 
dolomite comprising 25-68% of supratidal sediments in lagoons studied near Akumal (Ward, 
1975 cited in Weide, 1985). 
Initial and uptake phosphorus levels 

To determine the rate at which phosphorus was being absorbed by the limestone 
gravel, samples of 1 /limestone gravel not exposed to the sewage 2/limestone above the 
sewage water level of the wetlands and 3/limestone below the water level and thus exposed 
to the sewage for eleven months of system operation were analyzed for inorganic phosphorus 
content (Table 3-30). These results indicate that phosphorus enrichment has averaged some 6 
mg/kg (ppm) per year in the limestone exposed to sewage. Limestone prior to placement and 
limestone above the sewage level average 38.0 ± 2.9 mg/kg while limestone below the 
sewage level averaged 43.8 ± 1.7 mg/kg. 

Limestone in the first treatment cells of both wetland systems were marginally higher 
in phosphorus content than the limestone of the second cells, but the results are not 
statistically significant. In System 1, first cell limestone totaled 43.5 ± 3.7 mg P/kg while in 
the second cell, phosphorus content totaled 39.9 ± 3.7 mg P/kg. In wetland System 2, first 
cell limestone totaled 48.1 ± 2.5 mg P/kg while that of the second cell was 43.6 ± 3.4 mg 
P/kg (Table 3-30). 

Figure 3-39 presents the phosphorus starting value and uptake by limestone in 
the wetland systems during their first year of operation. Since limestone gravel averages 
1350 kg/m3, and there are 25 m 3 of limestone in System 1 and 41m 3 in System 2, we can 



147 
Table 3-30 Inorganic phosphorus content of limestone samples. 



Date Description # of Mean Standard 

collected samples phosphorus error of the 

mg/kg mean 

Aug 96 Limestone gravel not used in wetlands 3 40.3 ± 4.2 

Dec 97 Limestone above the sewage line 4 36.3 ± 4.35 

Aug 96 All limestone not exposed to sewage 7 38.0 ± 2.9 
+ Dec 97 (total of above 2 categories) 

Dec 97 All limestone exposed to sewage 20 43.75 ±1.68 

(composite of samples from all cells 

and systems) 

Dec 97 System 1, Cell 1 below sewage level 5 43.5 ±3.7 

Dec 97 System 1, Cell 2 below sewage level 5 39.9 ± 3.7 

Dec 97 System 2, Cell 1 below sewage level 5 48. 1 ± 2.5 

Dec 97 System 2, Cell 2 below sewage level 5 43.6 ±3.4 



148 













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149 

calculate that System 1 limestone totaled 33,750 kg and System 2 limestone totaled 55,350 
kg, for a combined weight of around 89,000 kg (8.9E7 g). Average enrichment in System 1 
limestone was 3.8 mg P /kg. Enrichment in System 2 limestone averaged 7.8 mg P/kg, for a 
total uptake of 570 g P/yr, or 47.5 g P/month. This is equivalent to 40 kg P ha" 1 yr" 1 uptake by 
the limestone in the wetlands on an areal basis. 

Phosphorus levels in influent water averaged 6.25 mg/1 and was 1.3 mg/1 in effluent 
water. So with 800 litters/day entering the system, phosphorus into the system was 150 
g/month, and after ET losses, discharge was 600 litters/day, phosphorus in discharge water 
totaled 23.4 g/month. The unaccounted for phosphorus, totaling 79.1 g/month was likely 
taken up by bacterial and plant biomass. 
Experiments on limestone P uptake 

In Table 3-31 and Figure 3-40 the reduction in phosphorus is reported from laboratory 
experiments where phosphorus solutions were mixed with Yucatan limestone in bottles. 
After ten days, phosphorus was reduced 28-63% when initial conditions were 5.6-1 1 1 mg 
P/liter. 

Field experiments where actual septic tank effluent was employed, showed 
56.9% reduction with a starting concentration of 5.1 1 mg P/l. In samples where the ratio of 
limestone gravel and effluent were kept nearly equal (comparable to conditions in the 
wetland units) reduction of phosphorus increased to 85.6% after 10 days (Table 3-31). 



150 
Table 3-31. Results from experiments on limestone uptake of phosphorus. 

Laboratory: 

1 " * " ' 

Sample Initial One day after Two days Four days Six days Ten days 

number loading loading Mg/1 P mg/1 P mg/1 P mg/1 P 

mg/1 P mg/1 P 



2-1 
2-2 
2-3 


5.6 
5.6 
5.6 


4.35 
4.35 
4.23 


4.35 
4.23 
4.29 


4 

4.12 

3.71 


3.65 
3.42 
3.31 


3.19 

2.9 
2.67 


Average 


5.6 


4.31±0.04 


4.29± 0.03 


3.94±0.12 


3.46±0.1 


2.92±0.15 


Percent 
Reductior 




23.0 


23.4 


29.6 


38.2 


47.9 


3-1 
3-2 
3-3 


11.1 
11.1 
11.1 


8.1 

8.62 

8.62 


8.16 
8.85 
8.85 


7.52 
7.75 
8.21 


7.23 
7.75 
8.25 


6.25 
6.66 
6.77 



Average 11.1 8.45±0.17 8.62± 0.23 7.83± 0.2 7.74± 0.29 6.56 ±0.16 



Percent 
Reduction 


23.9 


22.3 


29.5 


30.2 


40.9 


4-1 22.2 
4-2 22.2 
4-3 22.2 


18.6 
18.6 
18.6 


19.3 
19.5 
19.8 


19.3 
19.1 
23.1 


17.5 
17.7 
16.7 


16.2 
15.5 
16.5 



Average 22.2 18.6 ±0.0 19.5±0.15 20.5±1.3 17.3±0.32 16.0±0.31 



Percent 
Reduction 


16.3 


12.1 


7.7 


22.0 


27.7 


5-1 55.6 
5-2 55.6 
5-3 55.6 


46.9 
52.1 
53.7 


56.8 
53.7 
45.4 


46.4 
50.0 
53.7 


33.4 
63.0 
35.0 


29^8 
37.6 
33.9 



Average 55.6 51.0±2.04 51.9±3.41 50.0±2.1 43.8 ±9.62 33.8±2.25 











151 






Sample 


Initial 


One day after Two days Four days 


Six days Ten days 


number 


loading 
mg/lP 


loading 
mg/lP 


Mg/1 


P mg/lP 


mg/lP 


mg/lP 


6-1 


111.1 


106.2 


91.6 


103.0 


79.6 


37.7 


6-2 


111.1 


101.1 


108.7 101.8 


83.4 


42.7 


6-3 


111.1 


101.8 


97.3 


85.9 


77.6 


42.7 


Average 


111.1 


103.0±1.61 


99.215.04 96.9±5.51 


80.2+1.68 41.111.69 


Percent 




7.3 


10.7 


12.8 


27.8 


63.1 


Reduction 














Field studies: 












Sample 


Initial 


One day after 




Two Four 


Six 


Ten 30 days 


number 


loading loading 




days days 


days 


days mg/1 P 




mg/lP 


mg/lP 




mg/1 P mg/1 P 


mg/lP 


mg/lP 


7-1 


5.11 




3.3 


2.65 3.1 


2.1 


L55 0^85 


7-2 


5.11 




3.9 


3.75 3.6 


3.3 


2.8 1.95 


7-3 


5.11 




4 


4 3.55 


3.15 


2.25 1 


avg 


5.11 


3.7±0.2 


3.47± 3.42± 


2.8512.210.3 1.271 










0.41 0.16 


0.38 


6 0.34 


Percent 






27.3 


32.2 33.1 


44.2 


56.9 75.2 


Reduction 














7-4 


5.11 




1.45 


0.8 0.95 


0.75 


0.85 0.45 


7-5 


5.11 




3.05 


1.1 0.7 


0.85 


0.7 0.45 


7-6 


5.11 




1.15 


1.1 0.95 


0.75 


0.65 0.4 


avg 


5.11 




1.88± 


1.010.1 0.871 


0.781 


0.731 0.431 








0.59 


0.08 


0.03 


0.06 0.02 


Percent 






63.1 


80.4 83.0 


84.7 


85.6 91.5 


reduction 


,....„„ 
















152 














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153 

Water Budget 

Estimates of the water budget of the wetland treatment systems are given in 
Table 3-32 and Table 3-33. 

The results from the May 1997 study indicated that evapotranspiration rates are 
similar in wetland systems 1 and 2, since total evapotranspiration is 58% greater in System 2 
than System 1, and System 2 is 60% larger. With the system loading occurring in May 1997, 
on average 0.05 m 3 (9 gal.) [equivalent to 0.99 mm over the area] was discharged per day 
from wetland System 1 and 0.33 m 3 (85 gal.) [4. 1 mm] were discharged per day (Table 3-32). 

The data from the December 1997 measurements show that overall 
evapotranspiration was only 50% that of the summertime for wetland System 1 and 39% in 
wetland System 2. Discharge in December 1997 was 0.16 m 3 (42 gal.) [3.2 mm] per day from 
wetland System 1 and 0.3 m 3 (79 gal) [3.7 mm] from wetland System 2 (Table 3-33). 

Hydraulic loading of the wetland systems in May 1997 was equivalent to about 1.9 
inches/week for wetland System 1, and 2.8 inches of wastewater/week for wetland System 2. 

Under these conditions, ET losses were 90% of influent in wetland System 1 and 
59% in wetland System 2. Estimated hydraulic residence time in May 1997 was about 28.8 
days for wetland System 1 and 19.8 days for wetland System 2. The data indicate that 
hydraulic loading in December 1997 was similar in wetland System 1, but had dropped in 
wetland System 2 to 1.7 inches/week. Evapotranspiration losses were 41% in wetland 
System 1 and 38% in wetland System 2. 
Economic Evaluation 

Economic evaluations of the constructed wetlands vs. a "package plant" sewage 
treatment system built for a comparable number of residents in Akumal show that capital 



154 



Table 3-32 Daily water budget of wetland treatment systems, May 1997. 
Date Wetland Input from septic Evapotranspiration System 



system tank loss discharge 

mVday (gal/day) m 3 /day(gal/day) m 3 /day (gal/day) 



May 1997 System 1 0.34(88) 



0.29 (79) 



0.05 (9.) 



May 1997 System 2 0.79(205) 0.46(120) 



0.33 (85) 



See notes below Table 3-33. 









155 



Table 3-33 Daily water budget of wetland treatment systems, December 1997. 



Date 



Wetland Input from septic Evapotranspiration System 
system tank loss discharge 

m 3 /day (gal/day) m 3 /day(gal/day) m 3 /day (gal/day) 



December 1997 System 1 0.3 (87) 



0.14(361.) 



0.16(42) 



December 1997 System 2 0.48(127) 



0.18(48) 



0.3 (79) 



Notes on Table 3-32 and Table 3-33 



1. Water input from septic tanks 






Effluent from the septic tanks was estimated from their volume and measured inflow 
after they were pumped out. 

Wetland System 1 septic tank is 2.5 m wide x 4 m long x 1 m deep (to the discharge 
pipe), with a capacity of 10 m 3 (2600 gallons). Over the course of 9.5 days In May 1997, 
septic tank filled 0.32 m, or 3.2m 3 (832 gallons). This is a daily input of 0.34 m 3 (87.6 ' 
gallons). There were 3 people resident in buildings serviced by the septic tank, plus 3 people 
working in shops whose bathrooms are connected to the septic tank. These daytime workers 
are counted as 0.33 people, so a total of 4 people were serviced by the septic tank. Their 
daily wastewater production was 0.085 m 3 (22.1 gallons/day). 

^ In December 1997, septic tank of wetland System 1 filled 0.28 m, so inflow was 2.8 
m (739 gallons) over the course of 9.4 days. This is a daily input of 0.3 m 3 (78.6 gal). There 
were 3.5 people using the system (computed as above), so daily wastewater production was 
0.086 m 3 (22.5 gal) per person. 
Table 3-33 continued 



156 

The wetland System 2 septic tank is 2.3 m wide x 4.5 m long x 1. 15 m deep (to 
discharge pipe), a volume of 1 1.9 m 3 (3095 gallons). In 10 days of refill in May 1997, 7.87 
m (2046 gallons) of water entered the septic tank of wetland System 2. This is equivalent to 
0.787m or 204.6 gallons/day. During this period there were 7 people living in housing which 
the septic tank served. On average, wastewater production during this period was 29.2 
gallons/person/day for wetland System 2. 

In December 1997, this septic tank filled 4.51m 3 (1 191 gal.) over 9.4 days so daily 
inflow was 0.48m 3 (127 gal.). With 5 people on average using the system, this equals a daily 
wastewater production of 0.096 m 3 (25.4 gal) per person per day. 

2. System evapotranspiration 

Evapotranspiration (ET) was estimated from decreases in standpipe water levels 
during periods without discharge, input from septic tank. Inputs from direct rain were 
measured and this addition was factored into calculations of system ET. 

Porosity of limestone gravel in the wetlands was determined to be 35% through 
successive measuring of water required to fill a 20 liter bucket filled with the same grade of 
limestone used in the wetland. Since wetland System 1 is 50.6 m2 with a normal wastewater 
level of 0.55 m (with standpipe vertical) and a porosity of 0.35, total water capacity of 
wetland System 1 is 9.74 m 3 or 2,533 gallons. Wetland System 2 is 81.2 m 2 , with wastewater 
depth of 55 cm, porosity 0.35, giving a total system capacity of 15.6 
m (4,064 gallons). 

Standpipe water declines in May 1997 in wetland System 1 totaled 7.4 cm (0.074 m) 
over 4.5 days and in wetland System 2, standpipe water decline totaled 8.9 cm (0.089 m) 
over 5.5 days. Since there was no input into the wetlands during this period, and no 
discharge from standpipe overflow, this loss is equivalent to evapotranspiration in the 
system. Evapotranspiration in wetland System 1 was thus calculated to equal 1.31 m 3 (340 7 
gallons) over 4.5 days, or 0.29 m 3 (75.7 gallons) per day. Evapotranspiration in wetland 
System 2 was 2.52 m (657.6 gallons) over 5.5 days, or 0.46 m 3 (1 19.6 gallons/day) in May 
1997. Standpipe water declines in December 1997 averaged 5.7 cm in wetland System 1 and 
5. 1 7 cm over 9.4 days in wetland System 2. There were three rains totaling 1 . 8 cm over this 
period. Total evapotranspiration in wetland System 1 was thus 1.29 m 3 (340.6 gal) over 9.4 
days, or 0. 137 m (36.2 gal) per day. Evapotranspiration in wetland System 2 was 1 7 m 3 
(449 gal) over 9.4 days or 0.18 m 3 (47.8 gal) per day. 

3. Discharge of wastewater from the wetland treatment systems 
Average discharge of wastewater from the wetland systems was estimated from the 
difference between hydraulic inputs to the system and evapotranspiration losses from the 
system from wetland System 2. The data from the December 1997 measurements show that 



157 



Table 3-33 continued 

overall evapotranspiration was only 50% that of the summertime for wetland System 1 and 
39% in wetland System 2. Discharge in December 1997 was 0. 16 m 3 (42 gal.) [3.2 mm] per 
day from wetland System 1 and 0.3 m 3 (79 gal) [3.7 mm] from wetland System 2. 

Hydraulic loading of the wetland systems in May, 1997 was equivalent to about 1.9 
inches/week for wetland System 1, and 2.8 inches of waste water/week for wetland System 2. 
Under these conditions, ET losses were 90% of influent in wetland System 1 and 59% in 
wetland System 2. Estimated hydraulic residence time in May, 1997 was about 28.8 days for 
wetland System 1 and 19.8 days for wetland System 2. The data indicate that hydraulic 
loading in December 1997 was similar in wetland System 1, but had dropped in wetland 
System 2 to 1.7 inches/week. Evapotranspiration losses were 41% in wetland System 1 and 
38% in wetland System 2. 






158 

costs of package plants are more than twice that of the wetlands ($15,400 vs. $6,650) and 
maintenance costs are about ten times as great ($1,130 yr" 1 vs. $120 yr" 1 ) (Table 3-34 and 
Table 3-35). The wetlands are also expected to last longer, as machinery, especially in 
tropical conditions, has a far shorter replacement time. So on an amortized basis, the costs 
per year are even more divergent: over $2000 for the package plant vs. $330 for the wetland 
(even if the wetland only lasts 20 years as was assumed). 

Dependence on infrastructure is also greater for the package plant for since the 
system will not work without electricity to run grinders, pumps and blowers. The wetlands, 
relying on gravity flow for all movement of the sewage, and on filtration by the limestone 
and bacterial/vegetative action for treatment of the sewage, have mainly the requirement that 
filters be cleaned so that pipes do not clog. The package plant also requires a supply of 
chlorine for disinfection, since its hydraulic residence time (2-4 hours) is insufficient to 
achieve significant coliform bacteria reduction. 
Emergy Evaluation 

Emergy evaluations of the limestone constructed wetland system are calculated in 
Table 3-36 and summarized in Figure 3-41 a summary diagram of emergy flows in the 
wetlands. Wind is the largest environmental resource, but environmental inputs constitute a 
small flow (<1%) of total system emergy. Local materials, primarily Yucatan limestone, 
contribute some 2% of emergy used in the wetland treatment process and are the 
predominant source of system emergy use apart from the wastewater. The emergy contained 
in service and imported goods are less than 1% of total emergy. 

Emergy from local materials (Yucatan limestone, vegetation, mulch) constitute over 
60% of total emergy used for construction of the wetland treatment units. Operational costs 



159 



Table 3-34 Purchased materials and services used in construction of wetland systems, 
Akumal, Mexico. Costs are expressed in Mexican pesos (1996) and converted to U.S. dollars 
at the rate of 7.8 peso/$, which was the exchange rate in 1996 when systems were built. 



Item 


Quantity 


Cost per unit 


Cost 
(pesos) 


Cost (U.S. $) 


Native Materials: 










Limestone gravel 


72 m3 


1460 peso/12 m3 


8760 


$1123 


Limestone rock 


12 m3 


1460 peso/12 m3 


1460 


$187 


Sand 


21 m3 


800 peso / 7 m3 


2400 


$308 


Plants 


327 


variable, some free 


2200 


$282 


Imported Materials: 










Cement 


105 50-kg bags 


50 peso / bag 


5250 


$673 


Lime 


40 25-kg bags 


15 peso /bag 


600 


$ 77 


Steel rebar 


15 x 12-m 


48 pesos / piece 


720 


$ 92 


PVC pipe 


8x6-m, 10 cm 
dia. 


550 peso / piece 


4400 


$564 


Steel wire mesh 


131 m2, 3 mm dia. 




750 


$ 96 


Labor and Services: 










Backhoe rental 


20 m3 excavated 


450 peso / m3 


9000 


$1154 


Jackhammer rental 


25 m3 excavated 


450 peso / m3 


11250 


$1442 


Construction 
laborers 


3 people x 15 days 


70 peso / day 


3150 


$404 


Plumber, labor 


1 person x 1 week 


1500 peso /week 


1500 


$192 


Fuel and Power: 










Gasoline 


60 liters 


8 peso / liter 


480 


$ 62 


Total Construction 






51,920 


$6,656 


Cost 










Maintenance costs: 










Labor and Services: 










Labor 


104 hours/yr 


70 pesos/8 hrs 


910 


$117 


Annual 






910 


$117 


Maintenance Cost 












160 



Table 3-35 Purchased materials and services used in construction and annual maintenance of 
package plant sewage treatment system, Akumal, Mexico. Costs are expressed in Mexican 
pesos (1996) and converted to U.S. dollars at the rate of 7.8 peso/$, which was the exchange 
rate in 1996 when system was built. 



Item 


Quantity 


Cost per unit 


Cost 


Cost (U.S. $) 








(pesos) 




Native Materials: 










Sand 


7m3 


800 peso / 7 m3 


800 


$102.30 


Imported Materials: 










Concrete blocks 


125 blocks 


2.9 peso 


362 


$46.50 


Cement 


35 50-kg bags 


50 peso / bag 


1,750 


$224.40 


Rebar Steel 


7.5 pes x 12 m 


48 pesos 


360 


$46 


PVC Pipe 


32 x6m 


550 pesos 


17,600 


$2256 


Jet system 


includes blowers, 
grinders, motors 




70,200 


$9000 


Labor and Services: 










Construction labor 


80 people/days 


70 pesos 


5,600 


$718 


Excavation of 


includes steel pipe 




23,400 


$3000 


injection well 


liner 








Fuel and Power: 










Gasoline 


301 


8 pesos 


240 


$31 


Total - Construction 






120,312 


$15,425 


Cost 










Maintenance costs: 










Imported materials 










Chlorine 


10 kg 


40 pesos 


400 


$51.30 


Labor and Services: 










Labor 


150 hrs/yr 


50 pesos 


7500 


$961.50 


Fuel and Power: 










Electricity 


250 kWh/month 


79 pesos 


948 


$121.50 


Annual Maintenance 






8,848 


$1,134 


Costs 











161 



5.67 

Local > 1 
Materials, 

onstructiorA 




Limestone Wetland 
Treatment System 



Annual Flows in 
E15 sej/yr 



Water 354. 1 






Flow of money 



Figure 3-41 Diagram of emergy and money flows 
in wetland treatment systems, Akumal, Mexico. 
Units of diagram are E15 sej/yr. 



162 



Table 3-36 Em 


ergy analysis of tr 


le constructed 1 


imestone sewage 


wetlands. 




Note 


Item 


Raw Units 


Emergy per 


Solar 


EmDollars 








Unit 


Emergy 


(Thousands) 








sej/unit 


E15 












sej/yr 




ENVIRONMENT 












1 


Sunlight 


7.12E7J/yr 


1 


<0.001 




2 


Rain, chemical 


5.85E8J/yr 


1.82E4 


0.01 


0.01 


3 


Rain, 
geopotential 


2.58 E5 J/yr 


1.05E4 


O.001 




4 


Wind 


7.4E11 J/yr 


663 sej/J 


0.49 




5 


Land 


1.3 E8 J/yr 


2.9 E4 


<0.001 




Total (renewable 








0.48 


0.35 


resources) 












CONSTRUCTION 


(divided by 20 










INPUTS 


years) 










Local materials: 












6 


Gravel, 
limestone 


4.9E6 g/yr 


1.0E9sej/g 


4.9 


3.577 


7 


Rock, 
limestone 


7.35E5 g/yr 


1.0E9sej/g 


0.74 


0.54 


8 


Vegetation 


$14.1/yr 


1.9E12sej/$ 


0.03 


0.0058 


9 


Mulch 


4.5 E3 g/yr 


2.75 E8 sej/g 


O.001 


0.00007 


Subtotal (local 












construction 


items 6-9 






5.67 


4.14 


inputs) 












Imported goods 












and services 












10 


Cement 


0.3 ton/yr 


6.4E13sej/ton 


0.02 


0.0015 


11 


Lime 


5E4 g/yr 


1.0E9 sej/g 


0.05 


<0.001 


12 


Concrete block 


0.5 ton/yr 


6.4 E13 sej/ton 


0.03 


0.0022 


13 


Sand 


1.48E6g/yr 


1.0 E9 sej/g 


1.48 


1.08 


14 


Rebar steel 


151bs/yr 


8.9Ellsej/lb 


0.003 


0.0022 


15 


PVC pipe 


5.6E3 g/yr 


9.26E7 sej/g 


<0.001 


<0.001 


16 


Wire mesh 


12.5 Ib/yr 


8.9Ellsej/lb 


0.001 


<0.001 


17 


Gasoline 


1.2 E8 J/yr 


6.6E4 sej/J 


0.008 


0.0058 


18 


Rental of 
backhoe 


$57.7/yr 


1.9E12sej/$ 


0.11 


0.08 


19 


Jackhammer 
rental 


$72.1 /yr 


1.9E12 sej/$ 


0.14 


0.1 


20 


General labor 


2.4 E7 J/yr 


8.1 E4 sej/J 


0.002 


<0.001 


21 


Plumber 


$9.6/yr 


1.9E12sej/$ 


0.02 


0.01 


22 


Payment for 


$169/yr 


1.9E12sej/$ 


0.32 


0.23 


- ■ .- ...... . ... 


Goods 











163 



Note 


item 


Raw Units 


Transform ity 


Solar 


EmDollars 








Sej/unit 


Emergy 


(Thousands) 










E15 












sej/yr 




Subtotal imported 


Items 10-22 






2.18 


1.59 


goods and services 












Total inputs for 








7.85 


5.73 


construction 












HUMAN WASTE 












23 


Raw sewage 


3.94 E5 
gallons/yr 


8.767 Ell 
sej/gallon 


345.4 


252.13 


OPERATION 












24 


Maintenance 


$117/yr 


1.9E12sej/$ 


0.22 


0.16 


Total emergy 








354.1 


258.5 


OUTPUT (yield) 












25 


Treated 


5.17E10 


6.84 E6 sej/J 


354.1 


258.5 




wastewater 


J/yr 









* Column 6 (EmDollars) based on 1.37E12 sej/$, U.S. dollar/emergy ratio for 1996 (Odum, 
1996) 

Notes: 

1. SOLAR ENERGY 

Land area: 131.8 m2 

Insolation: 1 .8 E2 Kcal/cm2/yr (World Energy Data Sheet) 

Albedo: 0.30 

Energy (J) = (area) (avg insolation) (albedo) 

= (131.8m2) (1.8E2Kcal/cm2/yr) (E4 cm2/m2) (0.3) 
= 7.12E7 



2. RAIN, CHEMICAL POTENTIAL ENERGY 

Land area = 131.8 m2 

Rain = 9.44E-1 m/yr (IAM, U of Ga., 1988) 

ET = .9 (Lessing, 1975) 

Energy (J) = (area) (ET) (rain density) (Gibbs #) 

=131. 8m2 * (.9) * (1000 kg/m3) * (4.94 E3 J/kg) 
=5.85E8 J/yr 



164 



Table 3-36 continued 

3. RAIN, GEOPOTENTIAL 

Area = 131.8 m2 

Rainfall - 1.050 (Lessing, 1975) 

Avg Elev = 2m 

Runoffrate = .l(l-ET) 

Energy (J) = (area) * (%runoff) * (rain density) * (avg elevation) * (gravity) 

- 131. 8m2 * 0.1 * 1000 kg/m3 * 2 * 9.8 m/s2 

- 2.58E5 

4. WIND 

Based on method given in Odum, 1996, p. 294, with values of eddy diffusion and 

vertical gradient from Tampa, Florida and using wind of 1 m height 

(10 m)(I. 23 kg/cu m) (2. 8 cu m/m/sec) (3. 154E7 sec/yr) (2.3 m/sec/m)(130 sq m) 

= 7.4 Ell J/yr 

Transformity for wind from Odum, 1996 p. 186 

All of purchased goods and services (except annual maintenance) are divided by 20 

(anticipated life of wetland) to give emergy/yr 



5. LAND (EARTH CYCLE) 

Transformity = 2.9E4 sej/J (Odum, 1996, p. 186) 

Energy = (land area) (heat flow per area) 

heat flows for old stable areas is 1E6 J/m2/yr (Odum, 1996, p. 296) 

Energy = 130 m2 * 1E6 J/m2 = 1.3 E8 J/m2 

6. GRAVEL, LIMESTONE 

72 m3 at cost of 1460 pesos/12 m3 = 8760 pesos / (7.8 peso/U.S.$) = $1 123 
Transformity of limestone from Odum (1996, p. 310), emergy/gram: 1E9 sej/g 
Weight of limestone from Limestone Products, Newberry, FL (pers. comm.): 3000 lbs/m3 
72 m3 * 3000 lbs/m3 * 454 g/lb =9.8E7 g / 20 yrs - 4.9E6 g 
emergy in limestone gravel: 4.9E6 * 1E9 = 4.9E15 

7. ROCK, LIMESTONE: 

12 m3 of 5-10 cm rock at 1460 pesos/7.8 peso/$ = $187 

Transformity of limestone from Odum (1996, p. 310) emergy/gram: 1E9 sej/g 

Weight of limestone, 5-10 cm. rock, from Limestone Products, Newberry, FL (pers. comm ): 

2700 lbs/m3 

12 m3 * 2700 lbs/m3 * 454 g/lb =1.47E7 g / 20 yrs = 7.35 E5 g 



165 

Table 3-36 continued 

emergy in limestone gravel: 7.35E5 * 1E9 = 7.35E14 

8. VEGETATION 

approx. 2.5 plants per m2 planted, or 325 plants total; purchased plants for total 

of 2200 peso * $/7.8 peso = $282 /20 yrs = $14.1/yr * 5.2E12 sej/$ (emergy/dollar ratio from 

this study, see Table 3-64) = 7.33 E13 sej 

9. MULCH 

2.5 cm of sawdust and woodchip mulch (local and free) over 131 m2 = 3.28 m3 
transformity based on that for pulp wood 2.75E8 sej/g (Christensen, 1984) 
est. wt of mulch: 200 lbs * 454 g/lb = 9. lE4g / 20 yrs = 4.5E3 g/yr 
4.5E3*2.75E8=1.2E12 

10. CEMENT (LOCAL MANUFACTURE): 

105 bags @ 50 kg/bag = 5250 kg; price 50 peso/bag * 105 = 5250 peso 

5250 peso * $/7.8 peso = $673 

Transformity of concrete from Brown and McClanahan (1992, p. 27): 7E7 sej/g * 454 g/lb * 

2000 lb/ton = 6.356E13 sej/ton 

Concrete in wetland in cu yds: perimeter = 70 yds x 4"(. 1 1 yd) = 7.8 cu yd + bottom: 145 

yd2*4"(0.11yd)=16cuyd; 

23.8 cu yd * 500 lb/cu yd (est. from concrete company) * ton/2000 lbs = 5.95 tons concrete 

5.95 tons / 20 yr lifetime = 0.3 tons/yr 

11. LIME (LOCAL): 

40 bags @ 25 kg/bag = 1000 kg; price 15 pesos/bag * 40 bags = 600 peso * $/7.8 peso = $77 

1000 kg/20 yr= 50 kg/yr 

using same transformity as for limestone: 1E9 sej/g * 50 kg * 1000 g/kg = 1E13 sej 

12. CONCRETE BLOCK (LOCAL) 

250 blocks (40 cm x 20 cm x 15 cm) @ 2.9 peso/block = 725 peso * $/7.8 peso = $93 

using transformity of concrete from Brown and McClanahan (1992, p. 27): 7E7 sej/g * 454 

g/lb * 2000 lb/ton = 6.356E13 sej/ton 

est. wt of each concrete block = 20 lbs, total wt 20,000 lb * ton/2000 lb = 10 ton / 20 yrs = .5 

ton/yr 

.5 ton * 6.356E13 sej/ton = 3.2E13 sej 



166 



Table 3-36 continued 

13. SAND (LOCAL) 

21 m3 for 2400 peso total; 2400 peso * $/7.8 peso = $308 

est. wt of sand from Florida Rock Mines, Grandin, FL plant (pers. comm.): 3100 lbs/m3 

transformity of sand using Odum (1996, p. 310) for other Earth products: 1E9 sej/g 

21m3 * 3100 lbs/m3 * 454 g/lb = 2.96E7 g /20 yrs = 1.48E6 g 

1.48E6 g * 1E9 sej/g - 1.48E15 sej 

14. REBAR STEEL 

15 pes, 12 m length = 180 m; price 48 pesos/pc * 15 = 720 peso * S/7.8 = $92 

transformity of steel and iron products from Odum (1996, p. 193): 1.78E15 sej/ton * 

ton/2000 lb = 8.9Ellsej/lb 

est. wt of rebar: 15 pes * 20 lb/piece = 300 lbs / 20 yr lifetime - 15 lbs/yr 

15 1b*8.9Ell = 1.34E13sej/yr 

15. PVCPIPE 

transformity for plastic from Brown et al, 1992, p. 27: 9.26E7 sej/g 

weight of PVC pipe (est.) 14 kg / 6 m piece * 8 pc = 1 12 kg * 1000 g/kg = 1 . 12E5 /20 yr 

5.6E3 g/yr 

5.6E3 g/yr * 9.26E7 sej/g = 5.2 El 1 sej 

16. WIRE MESH: 

3 mm diameter, 131 m2; total price = 750 pesos * $/7.8 = $96 

transformity of steel and iron products from Odum (1996, p. 193): 1.78E15 sej/ton * 

ton/2000 lb = 8.9Ellsej/lb 

est. wt of wire mesh: 250 lbs / 20 yr lifetime = 12.5 lbs/yr 

12.5 lb * 8.9E11 - 1.34E13 sej/yr 

17. GASOLINE 

gasoline for concrete mixer: 60 liter @ 8 peso/liter (est.) = 480 pesos * $/7.8 peso = $62 

Transformity for motor fuel from Odum (1996, p. 308): 6.6E4 sej/J 

60 liter = 15 gal; bbl of oil = 42 gal; 

barrel of oil = 6.28E9 J/bbl * 15 gal/42 gal/bbl = 2.35E9 J / 20 = 1.2E8 J/yr 

1.2E8 J/yr * 6.6E4 sej/J = 7.9E12 sej 

**18. BACKHOE RENTAL 

450 peso per 1 m3 of excavation: approx. 20 m3 excavated = 9000 peso * $/7.8 peso = 

$1154 

$1 154 /20 yr - $57.7/yr * 1.9E12 sej/$ (Trujillo, 1998) 



167 



Table 3-36 continued 

**19. JACKHAMMER RENTAL 

450 pesos per 1 m3 of excavation: approx. 25 m3 excavated = 1 1250 pesos * $/7.8 peso = 
$1442 

$1442 / 20 yr = $72.1 /yr * * 1.9E12 sej/$ (Trujillo, 1998) 

20. LABOR 

Workers (general excavation and construction): 15 days * 3 people * 70 peso/day = 3150 

peso * S/7.8 peso = $404 

transformity for primitive (uneducated labor) from Odum and Odum, 1983: 8. 1E4 sej/J 

energy per person: 2500 Kcal/day * 41 86 Kcal/J * 45 days = 4.7E8 J/20 yrs = 2.4E7 J/yr 

2.4E7J*8.1E4sej/J=1.9E12 

21. PLUMBER LABOR 

7 days * 1 person = 1500 pesos * $/7.8 peso =$192 / 20 yrs = $9.6/yr * 1.9E12 sej/$(Trujillo, 
1998) 

22. PAYMENT FOR GOODS 

Monetary expenditures included limestone gravel: 8760 pesos, limestone rock: 1460 pesos, 
cement: 5250 pesos, lime: 600 pesos, sand: 2400 pesos, PVC pipe: 4400 pesos, steel 
rebar:720 pesos, wire mesh: 750 pesos, vegetation: 2200 pesos, and gasoline:480 pesos, for a 
total of 27,020 pesos / 7.8 pesos per dollar = $3464 U.S. dollars / 20 yrs = $173 per year 

1.9E12sej/$(Trujillo, 1998) 

23 HUMAN WASTE 

Yearly sewage = 36 people * 30 gal/day * 365 days/yr = 3.94 E5 gallons/yr 

Transformity based on emergy per person 

Since emergy per person in U.S. = 32 El 5 sej/yr and that for Mexico = 8 El 5 sej/yr (Odum et 
al, 1998), we will use an in-between average emergy since Akumal system is unlike typical 
Mexican one because of tourist economy: 16 E15 sej/yr 
Total wastewater per person = 50 gal/day * 365 days = 1 8250 gallons 

Transformity : 16 E15 sej / 1.825 E4 gallons = 8.767 El 1 sej/gallon 



168 

Table 3-36 continued 

24. OPERATION 

(est.) 2 hours/week * 52 weeks = 104 hr. for gardener/handyman @ 70 peso/8 hours = 910 

peso *$/7.8 peso = $117 

$117 * 1.9E12 sej/$(Trujillo, 1998) 

25. OUTPUT (yield): TREATED WASTEWATER 

Chemical potential of yearly inputs of raw sewage: 

Yearly treated wastewater = 1493.2 m3/yr - (1493. 2m3 * .3 (evapotranspiration loss)) = 

1045.2m3 

Water: (1045.2 m3/yr) * (10E6 g/m3) * (4.94 J/g) = 5.17E10 J 

Transformity: 354.1 El 5 sej / 5.17 E10 J = 6.85 E6 sej/J 

** in systems which don't have hard limestone excavation (e.g. beach sand sites) excavation 
costs are 6400 peso or 14,000 pesos less expensive; 14000 * $/7.8 peso = $1794 less 
expensive 



169 

total less than 3% of total construction emergy. 

The wetland system discharges less treated wastewater than it receives, since about 
30% are used in transpiration by the vegetation. 

By contrast, emergy analysis of a "package plant" sewage treatment system (Table 3- 
37 and Figure 3-42) built for a comparable number of residents in Akumal shows the far 
higher use of purchased services and imported resources that such highly technical systems 
use. There was very little use of renewable resources. The largest emergy flows (apart from 
wastewater) are that of imported goods and services, mainly representing the costs of 
imported machinery and high maintenance labor costs by technical personnel. 

Imported resources are more than 100 times higher than those of the constructed 
wetland) as might be expected as equipment and technical processing is substituted for the 
large buffering and retention the use of limestone gravel permits in the wetland systems. 

Operational costs of the package plant are around ten times higher than the wetland 
system ($1 100 vs. $117) and emergy in services are eighteen times higher (3.7 El 5 sej/yr vs. 
0.2E15sej/yr). 

The transformity of treated water from the package plant is 4.83 E6 sej/J, which is 
about 30% lower than the transformity for the wetland system (6.85 E6 sej/J), reflecting the 
greater quantity of discharged water in the package plant, since virtually all input water to 
the system is discharged. 

The empower density of the package plant is about three times higher than that of the 
wetland system (7.1 El 9 sej/ha vs. 2.5 E19 sej/ha) since such a highly technical system 
occupies requires less land area. 



170 



Sewage 




345.4 



0.004 




<0.001 



Operation 



1.91 , 1.83 




Package Plant 
Sewage Treatment 



Annual Flows in 
E15 sej/yr 



Water 356.2 



Flow of money 



Figure 3-42 Diagram of emergy and money flows 
in package plant sewage treatment systems, Akumal, 
Mexico. Units of diagram are E15 sej/yr. 



171 



Table 3-37 Emergy analysis of package plant sewage treatment system 



Note 


Item 


Raw 


Emergy per 


Emergy 


EmDollars 






Units 


Unit 
sej/unit 


E15 
sej/yr 


Thousands 


ENVIRONMENT 












1 


Sunlight 


2.75 E7 
J/yr 


1 


<0.001 


<0.001 


2 


Rain, chemical 


2.2 E8 

J/yr 


1.82E4sej/J 


0.004 


0.002 


3 


Rain, 
geopotential 


9.8 E4 
J/yr 


1.05E4sej/J 


<0.001 


<0.001 


4 


Land 


5 E7 J/yr 


2.9 E4 sej/J 


<0.001 




Total (Environment) 








0.004 


0.002 


CONSTRUCTION 


Divided by 20 










INPUTS 


years except 
machinery 
divided by 5 
years 










Imported goods and 












services 












5 


Cement 


0.3 ton/yr 


6.4 E13 

sej/ton 


0.002 


.001 


6 


Concrete block 


0.0625 
ton/yr 


6.4 E13 
sej/ton 


0.004 


.002 


7 


Sand 


5E5 g/yr 


1.0E9sej/g 


0.5 


0.4 


8 


Rebar steel 


7.5 Ibs/yr 


8.9 Ell 
sej/lb 


0.007 


.005 


9 


PVC pipe 


2.24E4 

g/yr 


9.26E7 sej/g 


0.002 


.001 


10 


Gas for concrete 
mixer 


6 E7 J/yr 


6.6E4 sej/J 


0.004 


.002 


11 


Machinery 


2.27E5 

g/yr 


1.25E10sej/ 
g 


2.8 


2.0 


12 


Excavation of 
injection well 


$150/yr 


1.9 E12 
sej/$ 


0.29 


0.2 


13 


"Jet system" 
cost 


$1800/yr 


1.9 E12 

sej/$ 


3.42 


2.5 


14 


General labor 


4.2E7 J/yr 


8.1 E4 sej/J 


0.003 


.002 


Total construction 








7.03 


5.13 


inputs 












HUMAN WASTE 












15 


Raw sewage 


3.94 E5 


8.767 Ell 


345.4 


252.13 






gallons/yr 


sej/gallon 







172 



Note 



Item 



Raw Emergyper Emergy EmDollars 

Units Unit El 5 Thousands 

sej/unit sej/yr 



OPERATION 












16 


Electricity 


UEIO 

j/yr 


1.74E5 sej/J 


1.9 


1.4 


17 


Maintenance 


$961.5/yr 


1.9 E12 

sej/$ 


1.83 


1.34 


18 


Chlorine 


1E4 g/yr 


l.lE9sej/g 


0.01 


.008 


Total Operation 








3.74 


2.73 


Total emergy 








356.2 


260 


OUTPUT (yield) 












19 


Treated 


7.38 E10 


4.95 E6 


356.2 


260 




wastewater 


J 


sej/J 






* Column 6 (EmDollars) based on 


1.37E12 sej/$, U.S. dollar/emergy ratio 


for 1996 (Odum, 


1996) 












Notes: 












1. SOLAR ENERGY 











Land area: 50 m2 

Insolation: 1.8 E2 Kcal/cm2/yr (World Energy Data Sheet) 

Albedo: 0.30 

Energy (J) = (area) (avg insolation) (albedo) 

- (50m2) (1.8E2Kcal/cm2/yr) (E4 cm2/m2) (0.3) 

- 2.75 E7 

2. RAIN, CHEMICAL POTENTIAL ENERGY 






Land area = 50 m2 

Rain = 9.44E-1 m/yr (IAM, U of Ga., 1988) 
ET = .9 (Lessing, 1975) 
Energy (J) = (area) (ET) (rain density) (Gibbs #) 
=50m2 * (.9) * (1000 kg/m3) * (4.94 E3 J/kg) =2.2 E8 J/yr 

3. RAIN, GEOPOTENTIAL 



Area = 50 m2 

Rainfall = 1.050 (Lessing, 1975) 

Avg Elev = 2 m 






173 

Table 3-37 continued 
Runoffrate = .l(l-ET) 

Energy (J) = (area) * (%runoff) * (rain density) * (avg elevation) * (gravity) 
= 50 m2 * 0.1 * 1000 kg/m3 * 2 * 9.8 m/s2 
= 9.8 E4 

4. LAND (EARTH CYCLE) 

Transformity - 2.9E4 sej/J (Odum, 1996, p. 186) 

Energy = (land area) (heat flow per area) 

heat flows for old stable areas is 1E6 J/m2/yr (Odum, 1996, p. 296) 

Energy = 50 m2 * 1E6 J/m2 = 5 E7 J/m2 

5. CEMENT 

35 bags @ 50 kg/bag = 1750 kg; price 50 peso/bag * 35 = 1750 peso 

1750 peso * $/7.8 peso = $224.40 

Transformity of concrete from Brown and McClanahan (1992, p. 27): 7E7 sej/g * 454 g/lb * 

2000 lb/ton = 6.356E13 sej/ton 

Concrete in system in cu yds: 6 cu yd; 

6 cu yd * 500 lb/cu yd (est. from concrete company) * ton/2000 lbs = 1.5 tons concrete 
1.5 tons / 20 yr lifetime = 0.75 tons/yr 

6. CONCRETE BLOCK 

125 blocks (40 cm x 20 cm x 15 cm) @ 2.9 peso/block = 362 peso * $/7.8 peso = $46.50 

using transformity of concrete from Brown and McClanahan (1992, p. 27): 7E7 sej/g * 454 

g/lb * 2000 lb/ton = 6.356E13 sej/ton 

est. wt of each concrete block = 20 lbs, total wt 2500 lb * ton/2000 lb = 1.25 ton / 20 yrs = 

.0625 ton/yr 

.0625 ton * 6.356E13 sej/ton = 3.97E12 sej 

7. SAND 

7 m3 for 800 peso total; 800 peso * $/7.8 peso = $102 

est. wt of sand from Florida Rock Mines, Grandin, FL plant (pers. comm.): 3100 lbs/m3 
transformity of sand using Odum (1996, p. 310) for other Earth products: 1E9 sej/g 
7m3 * 3 1 00 lbs/m3 * 454 g/lb = 0.98E7 g /20 yrs = 5E5 g 
5E5g* 1E9 sej/g = 5E 14 sej 

8. REBAR STEEL 

7.5 pes, 12 m length = 90 m; price 48 pesos/pc * 1 5 = 360 peso * $/7.8 = $46 



174 

Table 3-37 continued 

transformity of steel and iron products from Odum (1996, p. 193): 1.78E15 sej/ton * 

ton/2000 lb = 8.9Ellsej/lb 

est. wt of rebar: 7.5 pes * 20 lb/piece = 150 lbs / 20 yr lifetime = 7.5 lbs/yr 

7.51b*8.9Ell=6.7E12sej/yr 

9. PVCPIPE 

10 cm diameter, 32 pc x 6 m = 192 m; price 17,600 pesos * $/7.8 = $2256 

transformity for finished product, use average emergy/dollar ratio for Mexico: 5.5E12 sej/$ 

(source?) 

$2256/20 yr = $1 13 /yr * 5.5 E12 sej/$ = 6.2E14 

transformity for plastic from Brown et al, 1992, p. 27: 9.26E7 sej/g 

weight of PVC pipe (est.) 14 kg / 6 m piece * 32 pc =448 kg * 1000 g/kg - 4.48E5 /20 yr = 

2.24E4 g/yr 

2.24E4 g/yr * 9.26E7 sej/g - 5.2 El 1 sej 

10. GASOLINE 

gasoline for concrete mixer: 30 liter @ 8 peso/liter (est.) = 240 pesos * $/7.8 peso = $31 

Transformity for motor fuel from Odum (1996, p. 308): 6.6E4 sej/J 

30 liter = 7.5 gal; bbl of oil = 42 gal; 

barrel of oil = 6.28E9 J/bbl * 7.5 gal/42 gal/bbl =1 . 175E9 J / 20 = 6E7 J/yr 

6E7 J/yr * 6.6E4 sej/J = 4E12 sej 

11. MACHINERY 

2 blowers, 2 HP engine, grinder, 2 check valves, 2 u-joints 

estimated weight: 1500 lbs; divided by 3 years (expected life) = 500 lb * 454g/lb - 2.27E5 g 

Transformity = 1.25E10 sej/g (Odum et al, 1983, p. 432) 

12. EXCAVATION OF INJECTION WELL 
$3000/20 yrs = $150 

13. JET SYSTEM 

Jet system costs: including machinery, parts, bacterial media, filters: $9000 / 5 yr life = 

$1800 

* 1.9E12sej/$(TrujiIlo, 1998) 



175 

Table 3-37 continued 
14. LABOR 

Workers (general excavation and construction): 20days *4 people * 70 peso/day = 5600 peso 
*$/7.8 peso =$718 

transformity for primitive (uneducated labor) from Odum and Odum, 1983: 8.1E4 sej/J 
energy per person: 2500 Kcal/day * 4186 Kcal/J * 80 days = 8.37E8 J/20 yrs = 4.2E7 J/yr 
4.2E7J*8.1E4sej/J = 3.4E12 



15. RAW WASTEWATER 

Yearly sewage - 36 people * 30 gal/day * 365 days/yr = 3.94 E5 gallons/yr 

Transformity based on emergy per person 

Since emergy per person in U.S. - 32 E15 sej/yr and that for Mexico = 8 E15 sej/yr (Odum et 

al, 1998), we will use an in-between average emergy since Akumal system is unlike typical 

Mexican one because of tourist economy: 16 E15 sej/yr 

Total wastewater per person = 50 gal/day * 365 days = 18250 gallons 

Transformity: 16 E15 sej / 1.825 E4 gallons = 8.767 Ell sej/gallon 

16. ELECTRICITY 

estimate for operating system: 250 kWh/month = 3000 kWh/yr 

Transformity for electricity taken as mean global value - 173,681 sej/J (Odum, 1996, p. 305) 

Electrical energy = (3000 kWh) * (3.606E6 j/kWh) = 1.1E10 J 

17.. MAINTENANCE LABOR: 

estimated at 3 hrs/week of "technician" - 150 hrs/yr @ 50 pesos/hr = 7500 pesos *$ /7.8 
pesos = $961.50 
*1.9E12sej/$(Trujillo, 1998) 

18. CHLORINE 

10 kg used per year; 400 pesos cost; 

transformity - taken as equiv. to potassium chloride = 1 . 1E9 sej/g (Odum 1996 p 310) 

10kg*1000g/kg=lE4g/yr 



19. OUTPUT (yield): TREATED WASTEWATER 

Chemical potential of yearly inputs of raw sewage: 

Yearly treated wastewater = 1493.2 m3/yr 

Water: (1493.2 m3/yr) * (10E6 g/m3) * (4.94 J/g) = 7.38 E10 J 

Transformity: 356.2 E15 sej / 7.38 E10 J = 4.83 E6 sej/J 



176 

Receiving Wetland — Groundwater Mangroves 
Biodiversity 

Biodiversity in the mangroves near the discharge was determined by transects of 1000 
observations, made in December 1997 before effluent was released to the system. Total 
number of plant species was 17 (Table 3-2). The Shannon Diversity Index was 1.49 (base 2) 
and 0.45 (base 10) in December 1997 (Table 3-5). 

White mangrove (Laguncularia racemosa) is the most dominant plant in the wetland, 
accounting for some 84% of observations in the December 1997 transect and over 75% of 
tree stems in the discharge area. 
Mangrove Soils 

The mangrove soils had an average water content of 72% and dry weight averaged 
27.4% ± 1 .7% in six soil samples taken in December 1997 (Table 3-38). Bulk density in five 
samples taken to 31-35 cm depth with a 2.1 cm diameter soil corer, showed that bulk density 
averaged 0.060 ± 0.003 g/cm 3 (Table 3-39). 

Organic matter averaged 76.5 ± 0.8% in five soil samples (x 3 replicates) collected in 
December 1997 (Table 3-40). Variability amongst the five soil samples ranged from one 
sample with a mean of 79.4 ± 0.3% and the lowest organic matter content in a sample with a 
mean of 72.5 ± 0.1%. 

X-ray diffraction and scanning electron microscope analysis of the mineral portion of 
mangrove soil samples revealed the presence of calcite, amorphous silica, and the aragonite 
form of limestone. All the peaks on the X-ray diffraction analysis were small, with calcite 
being the most abundant mineral. Some slight presence of weddelite (calcium oxalate 



177 



Table 3-38 Wet weight/dry weight of soils in mangrove receiving wetland, December, 1997. 



Sample No. 



Wet Weight Dry weight Percent dry weight/wet weight 
kg kg 



1 


0.634 


0.129 


20.3 




2 


0.099 


0.029 


29.3 




3 


0.079 


0.024 


30.4 




4 


0.094 


0.029 


30.9 




5 


0.099 


0.029 


29.3 




6 


0.099 


0.024 


24.2 




Average 






27.4% ±1.7% 




± standard error of the 










mean 














178 



Table 3-39 Bulk density of soils in mangrove receiving wetland, December, 1997. 



Sample 

1 
2 
3 
4 
5 
Average ± standard error of the mean 



Volume Dry weight Bulk density 



grams/ cm 



cm 


grams 


473 


29 


468 


24 


439 


29 


443 


29 


439 


24 



0.061 
0.051 
0.066 
0.065 
0.055 
0.060 ± 0.003 












179 



Table 3-40 Organic matter content of soils in mangrove receiving wetland estimated from 
loss on ignition and mean values of the five soil samples, December 1997. 



Soil Sample Number of Mean percentage loss on ignition 

samples ± standard deviation of the mean 



1-1 3 73.2 ±0.1 

1-2 3 79.1 ±0.1 

1-3 3 79.4 ±0.3 

1-4 3 78.4 ±0.1 

1-5 3 72.5 ±0.1 

Mean± 76.5 ±0.8 
Standard error of 
the mean 



180 

hydrite, C 2 Ca0 4 - 2H 2 0) detected by the X-ray diffraction may have been a secondary 
product resulting from the preparation procedure (Dr. W. Harris, pers. comm.) 

Ash remaining after combustion for determination of organic matter was analyzed by 
inductive coupled plasma spectroscopy for calcium and magnesium content (Table 3-41). 

These results indicate that 41.9 +/- 1.3 percent is calcium and 3.2 +/- 0.1 is 
magnesium. Calcium thus constitutes a sizeable portion of the 23.5% non-organic portion of 
the mangrove soils, and if present as calcium carbonate would account for virtually all of the 
inorganic material. 

Depths of the mangrove wetland's organic soil were measured (Figure 3-43) to 
ascertain if there were limestone outcrops or cenotes in the vicinity of the outfall location 
which might prevent sufficient residence time to permit filtration and uptake of nutrients in 
the effluent. The results were mapped (Figure 3-44), showing that within a 15 meter radius of 
the outfall, soil depths varied from 33 to 55 cm before limestone rock was encountered. 
Average depth was 41.6 cm. No consistent pattern emerged, so an isopach could not be 
generated from the data, although many of the deepest soil depths were found close to the 
outfall site, and to its south (where soils averaged 48 cm deep along an axis 15 m long). 
Nutrients 

Sampling tubes were installed in the mangrove receiving wetland to determine water 
nutrient content before and after discharge. Sample point A was 1.1m upstream from the 
point of outfall, B was 1.1m downstream, C was 3.25 m downstream, D was 6.1 m 
downstream, and sample point E was 12 m southeast of discharge and closer to the edge of 
the wetland area. 

Before treated effluent discharge began nitrogen content of the mangrove soils 



181 



Table 3-41 Calcium and magnesium content of mangrove soil ash after combustion for 
organic content. Results determined by inductive coupled plasma spectroscopy. 



Sample 


Calcium 


Magnesium 




% 


% 


1 


40.1 


3.38 


2 


42.8 


3.46 


3 


39.1 


3.15 


4 


41.3 


3.15 


5 


46.4 


3.07 


Average ± standard error of the mean 


41.9 ±1.27 


3.24 ±0.08 









182 




u 

> 
o 

& 

c 
03 

£ 



o. 

03 
<u 

a. 

•o 

c 

03 

C 

o 

i 

l- 
— ' 

c 

! 

o 
2 

(50 

n 
u 

<U 
Q. 

1/3 

C 



"S ~ 



■ 



u 



x 8 



I 1 

u. < 



183 



-38 
--39 
--38 
--41 
--38 



w 



35 33 34 33 49 5,5^ 1 41 



Line of flow 



Thickness of peat in cm. 




33 34 33 35 



38-- 



51"- 



53 
44 



Discharge point for treated effluent 



1 



Scale 



6 m. 



Figure 3-44 Thickness of mangrove peat in the receiving wetland around 
the outfall pipe discharging effluent, December 1997. See Figures 1-8 for 
location of mangrove discharge point in Akumal. Mangrove soil samples 
were collected 1,3,5 and 10 m from discharge point in N,S, E and W directions 
(Tables 3-43 and 3-45). Water samples were collected at 1 m upstream (A), 
1m (B), 3m (C) and 6 m (D) downstream and 15 m (E) SE of discharge point 
(see Figure 1-9). 



184 

was 1.58% +/- .02% (Table 3-42), with a range from a low value of 1.44% N to a high of 
1.74% N. Table 3-43 presents nitrogen levels measured at specific distances from outfall in 
the mangrove wetland prior to and after discharge of treated effluent. 

Nitrogen levels measured lm from discharge point of the effluent showed about a 7% 
increase after 4 months of receiving the treated sewage (from 1 .68% to 1 .79% nitrogen). 
However, this increase may be due to other factors as the increase at 3m from discharge was 
1 1%, at 5m was 9% and 10m was 9% (Table 3-43). Nitrogen increase over pre-discharge 
levels totaled 18% for the South l-10m samples, 6% for the East l-10m, and 5% for both 
North and West l-10m. 

In December 1997, phosphorus levels in the mangrove soils averaged 0.32% +/- 
0.006% (Table 3-44). These nutrient concentrations may have been caused by anthropogenic 
additions to the site, as construction workers during this period used the wetland as an 
outdoor bathroom. In the mangrove soil samples from April - August 1997, phosphorus was 
measured at lower levels, ranging from 0.065% to 0.1 15% (Table 3-47). 

Table 3-47 shows analyses of mangrove soil from just before to four months after 
discharge commenced, which reveal increases in phosphorus levels of 5-10%.. At lm 
distance from outfall, P levels were 7% above those pre-discharge, and at 3m were 
unchanged, at 5m were +7%, and -9% at 10 m. Only in the South (+14%) and West (+3%) 
direction samples were phosphorus levels higher than pre-discharge. East and West direction 
soils samples were 5-6% lower (Table 3-47). 



185 



Table 3-42 Total Kjeldahl nitrogen content of soils in mangrove receiving wetland on 12 
December 1997 before discharge of treated effluent. 



December 1997 mangrove soil samples Total Kjeldahl nitrogen 

g/kg 

1 14.4 

2 14.4 

3 14.2 

4 16.2 

5 16.4 

6 15.8 

7 16.4 

8 15.2 

9 16.8 

10 16.6 

11 17.4 

12 16.0 

13 16.6 

14 15.6 

15 15.8 

mean ± standard error of the mean 15.9 ± 2.5 
Laboratory accuracy with nitrogen standard +3.1% 


















186 



Table 3-43 Total Kjeldahl nitrogen content of soils in mangrove receiving wetland before 
discharge (30 April 1998) and 2 months (3 July 1998), 3 months (3 August 1998) and 4 
months (2 September 1998) after discharge of treated effluent began 3 May 1998. 



Sample 
Location 
(Distance 

from 
discharge) 



#of 

Samples 

n 



30 Apr 

1998 

Total 

Kjeldahl 

Nitrogen 

g/kg 



3 Jul 1998 

Total 

Kjeldahl 

Nitrogen 

g/kg 



3 August 

1998 

Total 

Kjeldahl 

Nitrogen 



2 Sep 1998 

Total 

Kjeldahl 

Nitrogen 

g/kg 



Percent 
change 
from 30 

Apr 1998 
to 2 Sep 

1998 data 



East lm 


3 


17.7 + 0.2 


18.2 ±0.6 


19.0 ±0.4 


17.3 ±0.3 


-2% 


East 3m 


3 


15.410.4 


16.6 ±04 


16.8 ±0.3 


17.6 ±0.3 


+ 14% 


East 5m 


3 


16.2 ±0.5 


17.7 ±0.2 


18.7 ±0.4 


16.8 ±0.3 


+4% 


East 10m 


3 


15.1 ±0.6 


16.8 ±0.2 


18.0 ±0.3 


16.3 ±0.5 


+8% 


West lm 


3 


16.6 ±0.2 


17.8 ±0.3 


15.9 ±0.6 


18.1 ±0.4 


+9% 


West 3m 


3 


17.9 ±0.6 


17.8 ±0.2 


18.6 ±0.8 


18.6 ±0.1 


+4% 


West 5m 


3 


16.3 ±0.7 


18.0 ±0.3 


19.6 ±0.4 


18.1 ±0.6 


+11% 


West 10m 


3 


17.5 ±0.4 


16.3 ±0.3 


16.8 ±0.6 


17.0 ±0.3 


-3% 


North lm 


3 


16.8 ±0.7 


15.9 ±0.2 


17.0 ±0.6 


18.5 ±0.3 


+10% 


North 3 m 


3 


16.3 ±0.3 


19.3 ±0.1 


18.5 ±0.3 


17.5 ±0.2 


+8% 


North 5m 


3 


17.4 ±0.3 


18.2 ±0.5 


20.1 ±0.3 


17.7 ±0.2 


+2% 


North 10m 


3 


18.0 ±0.2 


18.4 ±0.3 


19.5 ±0.6 


18.0 ±0.3 


No change 


South lm 


3 


16.1 ±0.1 


17.4 ±0.4 


18.9 ±0.4 


17.8 ±0.4 


+11% 


South 3m 


3 


14.7 ±0.3 


17.6 ±0.6 


19.6 ±0.8 


17.6 ±0.5 


+19% 


South 5m 


3 


14.8 ±0.8 


16.9 ±0.4 


17.3 ±0.2 


17.5 ±0.3 


+19% 


South 10m 


3 


13.5 ±0.8 


16.7 ±0.3 


17.4 ±0.6 


16.7 ±0.2 


+24% 



Average lm 


12 


16.8 


17.3 


17.7 


17.9 


+7% 


Average3m 


12 


16.1 


17.8 


18.4 


17.8 


+ 11% 


Average5m 


12 


16.2 


17.7 


18.9 


17.6 


+9% 


Average 10m 


12 


16.0 


17.1 


17.9 


17.0 


+7% 


Average East 


12 


16.1 


17.3 


18.1 


17.0 


+6% 


Average West 


12 


17.1 


17.5 


17.7 


18.0 


+5% 


Average North 


12 


17.1 


17.9 


18.8 


17.9 


+5% 


Average South 


12 


14.8 


17.2 


18.3 


17.4 


+18% 



Laboratory accuracy with nitrogen standard - 4.2% (April & August 1998), -3.1% (July and 
September 1998) 






187 



Table 3-44 Phosphorus content of soils in mangrove receiving wetland on 12 December 
1997 before discharge of treated effluent. 



December 1997 mangrove soil samples 


Total phosphorus 




g^g 


1 


3.7 


2 


3.3 


3 


3.5 


4 


3.2 


5 


3.3 


6 


3.1 


7 


2.9 


8 


3.0 


9 


3.1 


10 


2.9 


11 


3.1 


12 


3.3 


13 


3.3 


14 


3.4 


15 


3.5 



Average ± standard error of the mean 3.2 ±0.1 

Laboratory accuracy with phosphorus standard +2.4%. 






188 



Table 3-45 Phosphorus content of soils in mangrove receiving wetland before and after 
discharge began May 3, 1998. 



Sample 


#of 


30 Apr 1998 


3 Jul 1998 


3 Aug 1998 


2 Sep 1998 


Percent 


Location 


samples 


Total 


Total 


Total 


Total 


change 


(Distance 


n 


Phosphorus 


Phosphorus 


Phosphorus 


Phosphorus 


from 30 


from 




g/kg 


g/kg 


g/kg 


g/kg 


Apr 1998 


discharge) 












to 2 Sep 




3 


0.88 ±0.03 






0.90 ± 0.03 


1998 data 


East lm 


1.08 ±0.03 


0.65 ±0.01 


+2% 


East 3m 


3 


0.86 ±0.02 


1.06 ±0.03 


0.87 ±0.07 


0.84 ± 0.07 


-2% 


East 5 m 


3 


0.90 ± 0.02 


0.94 ± 0.06 


1.04 ±0.04 


0.93 ± 0.05 


+3% 


East 10m 


3 


0.99 ± 0.03 


1.04 ±0.03 


0.91 ±0.07 


0.69 ± 0.03 


-30% 


West lm 


3 


0.88 ± 0.06 


0.91 ±0.05 


0.99 ±0.01 


1.00 ±0.03 


+12% 


West 3m 


3 


0.90 ± 0.07 


0.90 ± 0.05 


0.81 ±0.04 


0.96 ± 0.02 


+6% 


West 5m 


3 


0.89 ±0.01 


0.81 ±0.04 


0.98 ±0.13 


0.98 ±0.09 


+ 10% 


West 10m 


3 


1.13 ±0.09 


1.15±0.02 


0.87 ±0.06 


0.92 ± 0.05 


-18% 


North lm 


3 


0.76 ± 0.03 


1.03 ±0.01 


0.97 ± 0.04 


0.77 ± 0.03 


+1% 


North 3m 


3 


0.90 ± 0.04 


0.93 ± 0.04 


0.85 ±0.09 


0.71 ±0.04 


-21% 


North 5 m 


3 


0.84 ±0.07 


0.79 ± 0.05 


0.85 ±0.09 


0.81 ±0.03 


-3% 


North 10m 


3 


0.76 ± 0.04 


0.72 ± 0.04 


0.90 ± 0.09 


0.78 ± 0.03 


+3% 


South lm 


3 


0.99 ± 0.06 


1.03 ±0.07 


0.79 ± 0.04 


1.10 ±0.09 


+ 11% 


South 3 m 


3 


0.86 ±0.03 


1.00 ±0.07 


1.16 ±0.06 


1.00 ±014 


+16% 


South 5m 


3 


0.92 ± 0.03 


1.08 ±0.07 


1.05 ±0.08 


1.11 ±0.08 


+20% 


South 10m 


3 


0.98 ±0.05 


1.04 ±0.04 


1.15 ±0.06 


1.05 ±0.05 


+8% 


Average lm 


12 


0.88 


1.01 


0.85 


0.94 


+7% 


Average3m 


12 


0.88 


0.97 


0.92 


0.88 


No 
change 


Average5m 


12 


0.89 


0.91 


0.98 


0.96 


+7% 


Average 10m 


12 


0.96 


0.96 


0.96 


0.86 


-9% 


Average East 


12 


0.91 


0.87 


0.87 


0.84 


-6% 


Average West 


12 


0.95 


0.91 


0.91 


0.97 


+3% 


Average North 


12 


0.81 


0.89 


0.89 


0.77 


-5% 


Average South 


12 


0.84 


1.04 


0.94 


1.06 


+14% 



Laboratory accuracy with phosphorus standard +5.3% (April and August 1998) -6 5% (July 
and September 1998). 












189 

Hydrogeology of Coastal Zone 

Cross Section 

Figure 3-45 presents a systems diagram of the effluent-receiving salt-fresh wetland in the 
treatment system. The driving energy sources are sun and wind, while rain, tidal exchange, 
inland freshwater groundwater inflow and wastewater effluent contribute to the 
hydrology of the ecosystem. 

A geological cross-section of the coastal area (Figure 1-3) shows that the natural 
wetlands along the coast are located in the collapse karst zone where seawater and 
freshwater mix leading to dissolution of limestone. These wetlands are dominated primarily 
by mangrove-type vegetation except where limestone rocks provide elevated hammocks. 
Figure 1-9 presents a map showing the relationship of the wetland treatment units and the 
mangrove discharge and sampling areas in Akumal. 
Ground Water 

Measurements of water levels in three piezometer tubes in the mangrove receiving 
wetland enabled calculation of water flowlines. The difference between the three 
piezometers was slight, only 3/8 inch (0.95 cm) although they were separated by 
10-14 meters (Figure 3-46). Directions to the three piezometers were established from a 
reference point by surveyor transit level. These calculations showed that line of groundwater 
flow was approximately in an easterly direction. Changes in tidal range may be expected to 
change the gradient of flow but not its direction. 

Chart recorder data tracking changes in water levels in the mangrove wetland, in a 
nearby cenote (near to the edge but outside the wetland), and at the seaside at Yal-Kul lagoon 
in Akumal, showed that the mangrove soils had a large impact in lessening tidal fluctuations, 



190 










Figure 3-45 Systems diagram of the mangrove wetland receiving treated effluent. 



191 



N 



1/8 inch (0.32 cm) A 



Line of flow 



B-C 9.6 m 




C 

-3/8 inch 
(-0.98 cm) 



(datum) 



Figure 3-46 Potentiometric measurements of groundwater level in 
mangroves, December, 1997. Piezometers were located at A,B, and C. 
Survey transit level was located at point D. Flowlines calculated from 
data are approximately in easterly direction. 



192 

larger than would be expected by mere distance from the ocean. For example, chart 
recording data from May 27-28, 1997 (Figures 3-47 and Figure 3-48) showed that the cenote 
near the mangrove had total water level changes less than half as great as the ocean. Water 
level changes totaled 22.5 cm in the cenote while tidal flux at Yal-Ku totaled 48.5 cm. Also, 
the amplitude of the tides were less: 26 cm at Yal-Ku and 16.5 cm in the cenote. 

The mangrove wetland had considerably less water level changes than the cenote, 
despite the fact that both are nearly equidistant from the ocean (and in fact, the mangrove 
wetland where the chart recorder was placed is some 5-10 meters closer to the sea). For 
example, during December 10-14, 1997, total water level change in the mangrove was some 
17 cm as contrasted with 1 19 cm in the cenote, and 246 cm in tidal changes at Yal-Ku 
Lagoon (Figure 3-49, Figure 3-50, Figure 3-51). The greatest amplitude change in the 
mangroves was 7 cm while the shorter, sharper tidal fluxes in the cenote was as high as 21 
cm, and the tidal range at Yal-Ku reached 28 cm. 
Water Quality in Mangroves 
Total nitrogen 

Table 3-46 presents results of nitrogen analyses of water in the mangroves before and 
after discharge of treated effluent. 

Pre-discharge total nitrogen concentrations average around 4 mg/1 in the discharge 
area of the mangroves. After 3.5 months of receiving treated effluent, nitrogen 
concentrations in mangrove water were increased to 9-12 mg/1 in sites close to the discharge 
location. Increases of total nitrogen were 5-7 mg/liter in sampling sites 1-3 m from the 
discharge, but returned to background levels by 6 m distance (Table 3-46). 






193 



£ 



24_ 




> 

£ 20 — 
a> 



o 16- 

CO 



<D 12 







8 — 



o 
o 

CM 



o 
o 

CO 



27 May 97 



o 
o 

CN 



O 
O 
CN 



28 May 97 



Figure 3-47 Chart recorder water i^,»io : 

27-28 May 1997. dS ,n Cenote near we ^nd systems, 




25 May 97 



26 May 97 



27 May 97 28 May 97 



reS 3 2W S C !r;rr " ™ ter ICVdS * «*" '^on, show.ng Ma! 



195 




9 Dec 97 



10 Dec 97 



1 1 Dec 97 12 Dec 97 13 Dec 97 



Figure 3-49 Chart recorder water levels 
9-14 December 1997. 



in mangrove receiving wetland, 



196 



32- 




10 Dec 97 



1 1 Dec 97 



12 Dec 97 



13 Dec 97 



14 Dec 97 



Figure 3-50 Chart recorder water levels in cenote near wetland systems, 
10-14 December 1997. 

■ 



197 




10 Dec 97 



1 1 Dec 97 



12 Dec 97 



13 Dec 97 



Figure 3-5 1 Chart recorder water levels at Yal-lcu lagoon, showing tidal 
record, 10-14 December 1997. 



198 



Table 3-46 Total nitrogen in water of mangroves before and after discharge of treated 
wastewater. 



Before discharge 












Sample 
Location 


12 Dec 

1997 


3Mar 
1998 


30 Mar 
1998 


30 Apr 
1998 


Average ± 
standard 




Total 


Total 


Total 


Total 


error of mean 




nitrogen 


nitrogen 


nitrogen 


nitrogen 


Total 




mg/1 


mg/1 


mg/1 


mg/1 


nitrogen 












mg/1 


A, 1 m upstream 


8.2 


1.1 


1.6 


5.5 


4.1 ±1.7 


B, lm 
downstream 


7.7 


0.2 


2 


5.1 


3.811.7 


C,3m 
downstream 


10.3 


2.4 


2.8 


3.6 


4.8 ±1.9 


D,6m 
downstream 


5.9 


2.2 


3.1 


4.3 


3.9 ±0.8 


E, 12 m SE 


9.7 


2.3 


4.9 


9.2 


6.5+1 8 



After discharge: 






TAugl998 

Total 

nitrogen 

mg/1 


19 Aug 
1998 
Total 

nitrogen 
mg/1 




Sample 
Location 


31 May 
1998 
Total 

nitrogen 
mg/1 


30 Jun 1998 

Total 

nitrogen 

mg/1 


Average ± 
standard error 

of mean 

Total nitrogen 

mg/1 


A, 1 m upstream 


7.6 


7.3 


14.8 


13.5 


10.8 ±2.0 


B, 1 m downstream 


2.9 


1.7 


20.2 


10.1 


8.7 ±4.3 


C,3m downstream 


1.3 


9.8 


21.5 


15.7 


12.1 ±4.3 


D, 6 m downstream 


0.9 


3.5 


3.1 


3.0 


2.6 ±0.6 


E, 12 m SE 


4.9 


0.2 


3.2 


2.2 


2.6 ±1.0 



199 
Soluble reactive phosphorus 

Analyses of soluble reactive phosphorus in the mangrove water before and after 
discharge of treated effluent are presented in Table 3-47. 

Before discharge, soluble reactive phosphorus varied from 0.9 - 1.2 mg P/liter on 
average in mangrove water. After 3.5 months of discharge, locations 1 m distant had 
increased phosphorus levels by 2-3 mg/liter, but showed less increase at 3m from the 
discharge point. The sampling location 6m distant showed similar phosphorus concentrations 
to background levels in the mangrove (Table 3-47). 
Chemical oxygen demand 

Analyses of chemical oxygen demand (COD) in mangrove water are presented in 
Table 3-48. 

Mangrove water prior to discharge ranged from 60-160 COD mg/1. After 3.5 months 
of receiving treated effluent, sampling sites lm from discharge location had COD 
concentrations around 1 50 mg/1, and showed a decline in COD with distance from the 
discharge. By 6m distance, COD concentration was below that shown pre-discharge for that 
sampling location, and was below background levels of COD in the mangrove (Table 3-48). 
Total suspended solids 

Total suspended solids (TSS) were examined in the mangrove before and after the 
discharge of treated effluent (Table 3-49). Pre-discharge levels ranged from an average of 
280-360 with high variability (over 25% in some cases). After 3.5 months of receiving 
treated effluent, there was on average significant decline in suspended solids in the mangrove 
water. Sampling locations l-3m from the discharge had TSS levels 30-50% lower than they 



200 



Table 3-47 Soluble reactive phosphorus (SRP) in water of mangrove before and after 
discharge of treated wastewater. 

Before discharge: 

■ i n i 



Sample 12 Dec 3 Jan 24 Jan 3 Mar 30 Mar 30 Apr Average ± 
location 1998 1998 1998 1998 1998 1998 standard 

Total Total Total SRP Total SRP Total SRP Total error of 
SRP SRP mg/1 mg/1 mg/1 SRP mean 

Wl mg/1 mg/1 Total SRP 

mg/1 



A, lm 1.65 1.75 0.7 0.95 1.1 1.16 1.22 + 0.17 
upstream 

B, lm 1.55 1.05 1.35 1.05 0.88 1.4 1.21+0.11 
downstream 

C,3m 1.35 0.95 0.7 0.8 0.84 0.67 0.89 + 0.1 

downstream 

D,6m 1.05 1.8 0.6 1.15 0.66 1.16 1.07 + 0.18 

downstream 

E, 12mSE 2.1 0.85 0.95 0.6 0.65 0.54 0.95 + 0.24 



After discharge: 

Sample 31 May 30 June 1 Aug 1998 19 Aug 1998 Average ± standard error 
location 1998 1998 Total SRP Total SRP of mean 
Total SRP Total SRP mg/1 mg/1 Total SRP 
mg/1 mg/1 mg/1 

A, lm 3.54 4.1 3.69 3.63 3.74 ±0.12 
upstream 

B, lm 2.3 6.54 4.76 3.44 4.26 ±0.91 
downstream 

C,3m 0.34 1.67 4.03 3.44 2.37 ±0.84 

downstream 

D,6m 0.37 1.3 1.74 2.45 1.47 ±0.44 

downstream 

E, 12m SE 0.S6 0.44 1.03 2.17 1.05 ±0.39 



201 



Table 3-48 Chemical oxygen demand (COD) in water of mangrove receiving wetland, 
before and after discharge of treated wastewater 



— m 



— — — — — 



Before discharge: 

Sample location 3 Mar 1998 30 Mar 1998 30 Apr 1998 Average ± standard error of 
COD COD COD mean 

mg/1 mg/1 mg/1 COD 

mg/1 



A, 1 m upstream 


54 


70 


69 


64 ±5 


B, 1 m 
downstream 


48 


65 


144 


86 ±30 


C,3m 
downstream 


54 


76 


106 


79 ±15 


D,6m 
downstream 


129 


129 


203 


154 ±25 


E, 12 m SE 


189 


202 


93 


161 ±34 


After discharge: 











Sample location 31 May 1998 1 Aug 1998 19 Aug 1998 Average ± standard 

COD COD COD error of mean 

mg/1 mg/1 mg/1 COD 

mg/1 



A, 1 m 


102 


204 


150 


152 ±29 


upstream 










B, 1 m 
downstream 


112 


203 


129 


148 ±28 


C,3m 
downstream 


67 


211 


123 


134 ±42 


D,6m 
downstream 


55 


199 


76 


110 ±45 


E, 12 m SE 


82 


203 


133 


139 ±35 



202 

Table 3-49 Total suspended solids (TSS) in water of mangrove receiving wetland before and 
after discharge of treated wastewater 

Before discharge: 



Sample 3 Mar 1998 30 Mar 1998 30 Apr 1998 Average ± standard error of 
location TSS TSS TSS mean 

mg/1 mg/1 mg/1 TSS 

mg/1 



A, lm 275 277 330 294 ±18 
upstream 

B, lm 218 400 282 300 ±53 
downstream 

C,3m 139 378 424 314 ±88 

downstream 

D, 6 m 157 371 312 280 ±64 

downstream 

E, 12 m SE 209 435 435 360 ± 75 



After djschargej^ 



Sample 31 May 1998 30Junl998 1 Aug 1998 19 Aug 1998 Average ± 
location TSS TSS TSS TSS standard error of 



mg/1 mg/1 mg/1 mg/1 



mean 

TSS 

mg/1 



A, lm 74 112 328 145 195 ±58 

upstream 

151 176 173 167 ±7 

194 162 208 188 ±12 

248 198 228 225 ±13 

104 164 326 198 ±57 



B, lm 


55 


downstream 




C,3m 


73 


downstream 




D,6m 


49 


downstream 




E, 12 m SE 


52 



203 

had been pre-discharge. This was also true for the more distant sampling points (6m 
downstream and 12 m SE) and thus may reflect a general lowering in suspended solid 
content on the mangrove during this period of the year. There is, in any case, no increase in 
suspended solids content of the waters, as the locations closest to the discharge point are 
lower than other locations in the mangrove (Table 3-49). 
Coliform bacteria 

Coliform bacteria were measured in mangrove surface water before and after 
discharge (Table 3-50). 

In December 1997 and March 1998, coliform bacteria levels were 30,000 
colonies/ 100 ml. After discharge began on 3 May 1998, coliform levels close to the outfall 
were influenced by coliform concentration in the discharge effluent. When 700 colonies/ 100 
ml were counted in discharge water on 15 May 1998, only location A, 1 m upstream of the 
discharge showed elevated bacteria count (3500 colonies/100 ml). On 20 June 1998, when 
8700 colonies/ 100 ml were counted in discharge water, and on 3 August 1998 when 87,000 
colonies/ 100 ml were counted, elevated coliform levels were found in the monitoring 
locations 1-3 m from outfall, but point D, 6m downstream, was at or below background 
levels (Table 3-50). 
Salinity 

Salinity in the surface water of the mangrove measured December 21-22, 1997 (Table 
3-51) showed considerable variability, ranging from 7-15 parts per thousand (ppt). 

Over the course of a two day study, a smaller range was found in individual 
monitoring pipes, 1-2.5 ppt. At this time, the pumped tapwater in Akumal was 4.5 ppt, and 
salinity in the two wetland treatment systems varied from 3 to 4.5 ppt. 



204 



Table 3-50 Coliform bacteria in water of mangroves in 1998 after discharge of treated 
effluent. 



Sample location or type 


15 May 

Coliform 

MPN/100 ml 


20 June 
Coliform 

MPN/lOOml 


3 August 

Coliform 

MPN/lOOml 


Mean 

Coliform 

MPN/lOOml 


Discharge 
Effluent 


700 


8700 


83,000 


30,800 


Station A, 1 m upstream 


3500 


4000 


5300 


4267 


Station B, 1 m downstream 


120 


9000 


46000 


18373 


Stn. C, 3 m downstream 





3000 


6800 


3267 


Stn D, 6 m downstream 


820 


520 


40 


460 


Stn.E, 12 m SE 


19400 


510 


3060 


7657 



* measurements of mangrove water before discharge began: 
1 December 1997, 30,000 MPN/100 ml; 20 March 1997, 30,000 MPN/100 ml. 



205 
Table 3-51 Salinity in mangroves in 1997 before discharge of sewage effluent. 



Location 21 Dec 21 Dec 22 Dec 97 22 Dec 97 

0900 hr 1530 hr 1000 hr 1230 hr 

ppt ppt ppt ppt 



A, 1 m upstream 


13 


13 


14 


14 


B, 1 m downstream 


7 


8 


9.5 


9.5 


C, 3 m downstream 


9 


9.5 


10 


10 


D, 6 m downstream 


9 


9 


10 


10 


E, 12 m SE 


13 


14 


14.5 


I J 






206 

Salinity was measured at these locations monthly from March, 1998 through 
August 1998 (Table 3-52). 

After discharge began in early May 1998, salinity was around 2 ppt at locations A 
- D which were within 6 meters of the treated effluent. However, on 31 May 1998 when 
salinity was low (<0.5 ppt at station E), effluent with 2 ppt increased salinity (which 
averaged 1 .8 ppt at stations A-C). 

These data suggest that salinity was mostly lowered by the discharge of treated 
effluent. However, in periods of very low salinity in the mangrove (e.g. after heavy rains 
or during periods of high input of inland fresh groundwater) the treated effluent may be 
expected to raise salinity in the discharge area. 

Simulation of Water in Treatment Units and Mangroves 

A computer simulation model was developed to increase understanding of factors 
affecting water inputs and outflows in the wetland treatment units and mangroves. Figure 
3-52 presents systems diagrams of water in the treatment wetland units and the water in 
the mangrove receiving wetland with equations used in the simulation model. Figure 3-53 
shows the systems diagram with calibration values for storages and for flows along 
pathways. Table 3-53 gives the computer program for the simulation and Table 3-54 is 
the spreadsheet with calibration values for storages and flows used to calculate 
coefficients of the model. 

The treatment wetland units receives inputs of water from incident rainfall 
(J r ) that falls directly on the wetlands and sewage (J s ). Transpiration (k 2 ) is controlled by 
amount of water in the wetland (Q0 and its interaction with sunlight (Si), wetland 
biomass (B,), and the wind (w). Wetland biomass increase (k 8 ) is autocatalytic, driven by 



207 



Table 3-52 Salinity in mangroves in 1998. Discharge of treated effluent began May 
1998. 



Location 3 Mar 30 Mar 30 Apr 31 May 30 Jim 1 Aug 19 Aug 

PPt ppt ppt ppt ppt ppt ppt 



A, 1 m upstream 


9 


11 


12 


1.5 


2 


2 


2 


B, 1 m downstream 


7 


9 


10.5 


2 


2 


1.5 


2 


C, 3 m downstream 


5 


12 


14 


1.5 


2 


2 


1.5 


D, 6 m downstream 


5.5 


8 


10 


<0.5 


4 


2 


2 


E, 12 m SE 


5.5 


12.5 


13.5 


<0.5 


3 


5 


4 



Table 3-53 Salinity in mangroves in 1997 before discharge of sewage effluent. 



Location 21 Dec 21 Dec 22 Dec 97 22 Dec 97 

0900 hr 1530 hr 1000 hr 1230 hr 

Ppt ppt ppt ppt 



A, 1 m upstream 


13 


13 


14 


14 


B, 1 m downstream 


7 


8 


9.5 


9.5 


C,3m downstream 


9 


9.5 


10 


10 


D, 6 m downstream 


9 


9 


10 


10 


E, 12 m SE 


13 


14 


14.5 


15 



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210 

Table 3-53 Computer program in BASIC for simulation model of water budget in 
treatment wetland unit. 5 



'Water budget simulation model for 

treatment system 

4CLS 

5 SCREEN 1,0 

6 COLOR 15,1 

10 LINE (0,0X400, 300), 15, B 

15 LINE (0,60X400, 60) 

20 LINE (0, 120)-(400, 120) 

25 LINE (0, 180)-(400,180) 

30 LINE (0, 240)-(400, 240) 

35 LINE (0, 300X400, 300) 

50 dT = 1 

55 tO = 1 ' make equal to yr # 

60 TdO = .6 

65 SO =90 

70Q20 = .l 

75Q10-.1 

80 B10 = .2 

85B20 = .l 

86JrO = .01 

87JgO = .l 

95 S = 3000 

110Td = .68 

155Jr = 0! 

180B1 =2 

185B2 = 9 

190Q1-.16 

195 Q2 = 1 

196A-1 

205DMw(12),Jg(12),Js(12) 

223 FORI = 1 TO 12 

224 READw(I) 

225 NEXT I 

226 DATA 

5,6.6,43,44,5.6,5.4,4.5,3.6,4:1,4.4,5.9,6.7 
230 FOR I = 1 TO 12 

232 READJgfT) 

234 NEXT I 

236 DATA 

0.254,0.2,0.2,0.2,0.6,0.47,0.29,0.33,0 47 4 
4,0.22,0.21 

238 FORI = 1 TO 12 

240 READJsO) 

242 NEXT I 



244 Data 

.034,0.034,0.034,0.034,0.022,0.022,0.022,0. 

022,0.022,0.034,0.034,0.034 

275 K2 = .000001 6666# 

282 k4= 1.012625* 

285 K5 = .0000O2S 

290 K7 = .520833 

292 K8 = . 73752 

294 K9 = . 000001 14# 

295 klO = .0000006752 
300 Kll =.000457 
305K12 = .000169# 
306 kl = .02902# 
3091=1 

320 PSET ((t+y • 365) / 10 * tO, 60 - S / 
SO), 2 

325 PSET ((t + y * 365) / 10 * tO, 160 - Ql / 
Q10), 1 

330 PSET ((t + y * 365) / 10 * tO, 120 - Q2 / 
Q20), 2 

335 PSET ((t + y * 365) / 10 * tO, 160 - Bl / 

B10), 4 

340 PSET ((t + y * 3651/ 10 *t0, 180 -B2/ 

B20), 3 

350 PSET ((t + y * 365) / 10 * tO, 60 - Jr / 

Jr0),2 

360 PSET ((t + y * 365) / 10 * tO, 1 80 - Jg(I) 
/Jg0),4 

380 S = 3000 + 1500 • SIN(t * .01 93 - 90) ' 
ANNUAL SINE WAVE SUNLIGHT 
385 IF S < THEN S = 
390S1=S/(1 + K7*Q1 *Bl*w(T)) 
395S2 = S/(l+K8*Q2*B2*w(I)) 
400 Jts = Ql -.16 

403IFQl<.16THENx = 

405IFQl>.16THENx=l 

415 dQl =Js(I) + Jr- Jts-(K2*S1 *B1 * 

Ql *w(T;) 

418dQ2 = Jr + (x*kl * Ql) + Jgfl) - (k4 * 

(Q2 / A - Td)) - (K5 * S2 * B2 * w(I) * Q2) 

425 dBl = (K9 * SI * Ql * Bl * wfl)) - 

(K11*B1) 






211 



Table 3-53 continued 

428 dB2 = (klO * S2 * Q2 * B2 * w(D) - 
(K12*B2) 

430ET1=(K2*S1 *B1 *w(I)*Ql) 

431 ET2 = (K5 * S2 *B2 * w(I) * Q2) 

440 Bl = Bl + dBl *dT 

442 Ql = dQl * dT + Ql 

444 Q2 = dQ2 * dT + Q2 

446B2 = dB2*dT + B2 

450 TJr = TJr + Jr * dT 

454 TJs = TJs + Js(T) * dT 

456 TET1 = TET1 + ET1 * dT 

458TJts = TJts + Jts*dT 

460 TET2 = TET2 + ET2 * dT 

560 prob = RND 

562 Jr = 

570 IF t <= 30.42 AND prob < .164 THEN 

Jr = .0156 

580 IF (t > 30.42 AND t <= 60.84) AND 

prob <. 131 THEN Jr = . 0103 

590 IF (t > 60.84 AND t <= 91.26) AND 

prob < .072 THEN Jr = .01 92 

600 IF (t> 91.26 AND t <= 121.68) AND 

prob < .059 THEN Jr = .0229 

610F (t> 121.68 AND t<= 152.1) AND 

prob <. 158 THEN Jr = . 0348 

620 IF (t > 152.1 AND t <= 1 82.52) AND 

prob<26THENJr = .0182 

630 IF (t > 182.52 AND t <= 212.94) AND 

prob < .224 THEN Jr = .0129 

640 IF (t > 212.94 AND t <= 243.46) AND 

prob < .256 THEN Jr = .01 29 

650 IF (t > 243.46 AND t <= 273.78) AND 

prob < .322 THEN Jr = .0153 

660 IF (t > 273.78 AND t <= 304.2) AND 

prob < .312 THEN Jr = .01 48 

670 IF (t > 304.2 AND t <= 334.62) AND 

prob < .253 THEN Jr = .0097 

680 IF (t > 334.62 AND t <= 365) AND 

prob < .22 THEN Jr = .0085 

690 IF (y > 5 AND y < 10) THEN Jr = Jr * 

700 IF t <= 30.42 THEN I = 1 

702 IF (t > 30.42 AND t <= 60.84) THEN I 

704 F (t > 60.84 AND t <= 91.26) THEN I 



706 F (t > 91.26 AND t <= 121.68) THEN I 

= 4 

708 F (t > 121 .68 AND t <- 152. 1) THEN I 

= 5 

710 F (t > 152.1 AND t <= 182.52) THEN I 

= 6 

71 2 F (t > 1 82.52 AND t <= 21 2.94) THEN 

1 = 7 

714 F (t > 212.94 AND t <= 243.46) THEN 

1 = 8 

716 F (t> 243.46 AND t <= 273.78) THEN 

1 = 9 

71 8 F (t > 273.78 AND t <= 304.2^1 THEN I 

= 10 

720 F (t > 304.2 AND t <= 334.62) THEN I 

= 11 

722 F (t > 334.62 AND t <= 365) THEN I 

= 12 

1000t = t + dT 

1010 Ft< 365 GOTO 320 

1020y = y+ 1 

1030 1 - 1 

1040Fy<=10GOTO320 









212 



Table 3-54 Spreadsheet for calculation of coefficients in water bydget simulation model 
of treatment units and mangroves. 



Sources: 

Sunlight S= 



3000 kcal/m2/day 



Calibration States: 

Unused sunlight, treatment wetland 

S1= 500 kcal/m2/day 

Unused sunlight, mangrove wetland 

S2= 50 kcal/m2/day 

Tide level Td= 0.68 m3/m2 

Sewage input 

Js= 0.034 m/m2/day 

Rain Jr= 0.00302 m/m2/day 

Inland GW Jg= 0.3 m/m2/day 

Wind w= 5 m/sec 

Depth of water in treatment wetland 

Q1= 0.16 m 

Depth of water in mangrove wetland 

0.2= 1m 

Biomass, treatment wetland 

B1= 12kg/m2 

Biomass.mangrove wetland 

B2= 16 kg/m2 



flow (qty) 

k1 = 
0.008 k2= 



Flows per day: 
Calculations of coefficients 

Outflow from treatment wetland 

k1 * (Q1 - Qthreshold) = 
transpiration in treatment wetland 

k2*B1*Q1*S1V = 
Exchange between mangrove surface water and groundwater 
k4*((Q2/A) -Td) = ((Jr + Jts + Jg - (k5*B2*S2*W*Q2)) k4= 

k4*((Q2/A) -Td) = 0.32404 

transpiration in mangrove wetland 

k5*B2*Q2*S2*w = 0.008 k5= 

Unused sunlight, treatment wetland 

k7*Q1*B1*w = 500 500 k7= 

Unused sunlight.mangrove wetland 

k8*Q2*B2*w = 50 k8= 

Biomass increase, treatment wetland 

.k9*S1*Q1*B1*w = 5.48E-03 k9= 

Biomass increase, mangrove wetland 

k10*S2*Q2*B2*w = 2.70E-03 k10= 

Respiratory losses, treatment wetland 

k11*B1= 5.48E-03k11 = 

Respiratory losses, mangrove wetland 

k12*B2 = .0027 2.70E-03k12= 



0.02902 
1.67E-06 
1.012625 

0.000002 
0.520833 
0.7375 
1.14E-06 
6.75E-07 
0.000457 
0.000169 



213 

sunlight, wind, water levels, and the quantity of existing wetland biomass. Respiratory 
losses (kn) are a function of quantity of the biomass. Water exits the system by two 
methods: from transpiration from the wetland plants, and by outflow of treated 
wastewater (ki). Because of the density of plants, evaporation and plant uptake are 
minimal and have been omitted from this aggregated model. Treated sewage (kj) 
overflows out drainage pipe and leaves the wetland for the mangrove when the holding 
capacity of the treatment unit is exceeded (X in switch =1). 

The water inputs to the mangroves are direct incident rainfall (J r ), treated 
wastewater outflow from the treatment wetland units (J ts ), and groundwater input (J g ) and 
tidal inflow fa) when the water level of the mangrove (Q 2 ) is lower than that of the tides 
(Td). Water outputs are from transpiration (k 5 ) by the mangrove vegetation and tidal 
exchange fa) when mangrove water level exceeds sea level. Mangrove biomass grows 
(k 10 ) by an autocatalytic process, the energy drivers being sunlight (S 2 ), wind (w), 
available fresh water (Q 2 ) and its own biomass state (B 2 ). Mangrove biomass losses 
through plant respiration and animal consumption (k ]2 ) are a function of the quantity of 
biomass. 

The model was calibrated and its sources programmed with seasonally varying 
data from available literature on climatic factors (temperature, humidity, rainfall, tidal 
range, wind, evapotranspiration, groundwater flow) in the Yucatan (Appendix B). 
Groundwater discharge becomes more important in months with heavy rain, and treated 
effluent decreases at the same time of year (the off-peak tourist summer season). In the 
dry season, sewage inputs are greater and rainfall is decreased. 



214 

Simulation of the model under normal anticipated conditions (Figure 3-54) 
shows that treatment wetland biomass increases more rapidly than the mangrove biomass, 
though the constructed wetland reaches equilibrium (when rate of primary productivity 
equals respiration) at a lower value than the mangroves. Water levels remain fairly 
constant in the treatment wetlands since effluent discharge to mangroves occurs when the 
limestone is saturated, however there is a small annual elevation due to peak tourist 
season loading. Sewage inputs are an order of magnitude greater than rainfall inputs. 
Mangrove water levels reflect the influence of the large inland groundwater discharge 
during the summer/fall and inputs of treated sewage effluent are of the same order of 
importance as groundwater from inland sources. 

Simulation runs were conducted for extreme conditions (Appendix B). If sewage 
loading is increased ten-fold due to increased population use of the treatment system, 
there is rapid growth of wetland biomass and the mangroves show higher standing water 
levels (Figure 3-55). If inland development has eliminated groundwater flow to the 
mangroves, this results in lowering mangrove water levels, and decreasing mangrove 
growth (Figure 3-56). Hurricane events bring high rain, wind, and tidal levels, resulting 
in loss of half of both treatment wetland and mangrove biomass. Wetland vegetation 
recovery is more rapid than mangrove, but that overall both ecosystems may take 5-10 
years to fully restore biomass after a large hurricane (Figure 3-57). 

Notes on literature values used to estimate storage values and pathway flows in 
the water budget simulation model are given in Appendix B. 






215 










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| 

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-o 

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216 



AAAAAA/W 



RainfaN 
Mangrove biomass 



Mangrove water level 



.. . . ••■■ 



Wetland biomass 

Wetland water level 



Groundwater flow 



Simulation run 2 



Time > 



Figure 3-55 Simulation of water budget for wetland treatment unit and 
mangroves with increase of wastewater loading (10 times higher) 
Scale: sunlight 5000 Kcal/m 2 /day, biomass 20 kg/m2, water levels 1 5 m 
water inflows lm/day. 



217 



A/WWWYA 



. Rainfall 
Mangrove biomass 

Mangrove water level 



Wetland biomass 
Wetland water level 



Groundwater flow 



Simulation run 3 



Time 



Figure 3-56 Simulation of water budget for wetland treatment unit and 
mangroves with loss of groundwater inflow. Scale: sunlight 5000 
Kcal/m /day, biomass 20 kg/m2, water levels 1.5 m, water inflows 
lm/day. 






218 



A A A A A A A A A 

1 \j \J \J \J \J \J \J \J 



-*-" ~">—r^— « ■- -v~ 



Mangrove biomass 



Rainfall 

188m a— a ■ ~-. 



Mangrove water level 



Mangrove biomass 



Wetland biomass _., — ~. 

Wetland water level 



Wetland biomass 



Groundwater flow 



Simulation run 4 



Time 



Figure 3-57 Simulation of water budget for wetland treatment unit and 
mangroves with hurricane event at year 5. Scale: sunlight 5000 Kcal/m 2 /day 
biomass 20 kg/m2, water levels 1.5 m, water inflows lm/dav. 






219 
Regional Potential of Wastewater Treatment System 

Definition of Coastal System 

For purposes of estimating the regional role of the new wastewater treatment 
systems, a square kilometer area around Akumal was defined (Figure 3-58). Data 
collected from the homeowner's association in Akumal combined with interviews 
permitted an assessment of the environmental flows and support systems for this area. 
Judging from the pattern of current development, this area may contain 15 private houses 
and four hotels/condominium complexes, with a total resident population of 225-250 
(permanent residents plus tourists). 
Emergy Evaluation 

For this scenario, inputs to this area are diagrammed in Figure 3-59 and evaluated 
in Table 3-55. With the use of transformities from Table 2-1, emergy and emdollars were 
calculated in the last two columns. 

The largest renewable source emergy flows are those of inland groundwater and 
hurricanes. Tourism revenues (income) are the largest imported emergy flow, followed 
by imported goods, petroleum products and building materials (limestone, sand, 
concrete). Local services are about 25% of tourist revenues (Table 3-55). In aggregate, 
natural emergy from renewable natural resources is about 39% of total emergy flows. 

Inflows are grouped in categories in Figure 3-60 and used to calculate the indices 
shown in Table 3-56. Empower density is 1 .2 E16 sej /ha /yr. Service emergy compared 
to free energy is 0.32. Imported emergy flows are somewhat greater than local ones as the 
nonrenewable / renewable resource ratio is 1.22. The investment ratio of 1.49 is far lower 
than the United States, where it averages 7 (Odum, 1996). The sej / money flow ratio is 



220 
















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221 



Table 3-55 Emergy evaluation table of 1 -square-kilometer of developed coastline, 
Akumal, Mexico (see Figure 3-58). 



Note 


Item 




RENEWABLE RESOl 


1 
2 


Sunlight 
Rain 


3 
4 
5 
6 


Rain transpired 
Rain, geopotential 
Wind, kinetic 
Hurricanes 


7 


Waves 


8 


Tide 


9 
10 


Earth cycle 
Inland water flow 


11 


Pumped groundwater 



12 
13 



Subtotal (items 2 + 6 + 9+10) 

NON-RENEWABLE RESOURCES 

Loss of soil due to development 
Loss of vegetation due to development 
Subtotal (items 12+13) 



Raw Units 


Transformity 


Solar 


EmDollars 




(sej/unit) 


emergy 
E18sej 




4.54 E13 J 


1 


<0.001 


<0.001 


5.5 E12 


1.544 E4 


0.09 


62.0 


4.46 E12 J 


1.544 E4 


0.07 


51.1 


2.65 Ell 


8.88 E3 


<0.001 


<0.001 


2.7 E9 


6.63 E2 


<0.001 


<0.001 


1.14E13 


9.579 E4 


1.09 


796 


7.88 E6 


2.59 E4 


<0.001 


<0.001 


7.53 E5 


2.36 E4 


<0.001 


<0.001 


1E12 


2.9 E4 


0.03 


21.2 


7.41 E13 


4.8 E4 


3.54 


2,584 


4.28 Ell 


4.8 E4 


0.02 


15.0 



4.77 



3,482 



4.24 Ell 


7.37 E4 


0.031 


22.6 


4.7E11 


2E5 


0.094 


68.6 






0.13 


95 



14 



15 
16 
17 
18 
19 
20 
21 
22 
23 



LOCAL SERVICES 
Local labor and services 
+ '/2 0fitem22 
Subtotal 

IMPORTED GOODS AND SERVICES 

Forest products 

Limestone, gravel, sand 

Food 

Gas 

Petroleum products 

Electricity 

Imported Goods 

Capital investments 

Tourism 

Subtotal (items 15-23) 

Total 



7.68 E5$ 1.88 E12 



1.44 
0.13 
1.57 



* Column 6 (EmDollars) based on 1.37E12 sej/$, U.S. dollar/emergy ratio for 1996 



1,146 



5.09 E12 


3.49 E4 


0.2 


146 


1.53 Ell 


8.98 E6 


1.4 


1,022 


8.6 Ell 


8.5 E4 


.007 


51 


6.96 E4 


4.8 E4 


<0.001 


<0.001 


1.84 E13 


6.6 E4 


1.21 


880 


2.37 E12 


1.74 E5 


0.4 


292 


7.02 E5$ 


1.88 E12 


1.32 


885.4 


1.375 E5$ 


1.88 E12 


0.25 


183.5 


4.9 E5$ 


1.88 E12 


0.92 


2,476.7 






5.71 


4,168 






12.05 


8,891 



222 

Table 3-55 continued 

Notes: 

1 SUN 

Solar exposure of 2381 hours/year (Viguera et al, 1994) 
area = 1E6 m2 

avg insolation: 1.55 E2 kcal/cm2/yr (Brown et al, 1992) [taken as equal to that of Nayarit, Mexico] 
albedo = .3 

Energy = area * avg insolation * (1 - albedo) = 1E6 m2 * 1.55E2 kcal/cm2 * E4 cm2/m2 *.7 * 4186 J/kcal 
= 4.54E13 J 



2 RAIN, TOTAL 

Average rainfall at Puerto Moreles is 1 123 mm ((Ibarra and Davalos, 1991) for Puerto Moreles, Q.R. 

and at Tulum is 1 104 mm (Viguera et al, 1994). Therefore, a value of 1 1 14 mm was used 

transformity = 15,444 sej/J (Odum, 1996 p. 186) 

land area = 1E6 m2 

rainfall = 1.114 m 

Rain, total = area * rainfall * Gibbs # = (1E6 m2) * (1.1 14 m) * 1000 kg/m3 * 4.94E3 J/kg = 5.5E12 

3 RAIN, TRANSPIRED 
land area = 1E8 m2 
rainfall = 1.114 m 

ET = 0.9 (Viguera et al, 1994), given as % of rainfall = .81 
Rain, transpired = area * ET * rainfall * Gibbs # 

=lE6m2 * 1.114m * .81 * 1000kg/m3 * 4.94E3 J/kg =4.46E12 

transformity (Odum, 1996 p. 186): 15,444/J 

4 RAIN, GEOPOTENTIAL 
Transformity - 8.888E3 (Odum, 1996, p. 186) 

Energy = area * %runoff * rainfall * average elevation * gravity 

= 1E6 m2 * [(1-ET)= .81]* 1.1 14 m * 1000 kg/m3* 3 m * 9.8 m/s = 2.65 El 1 

5 WIND 

Average wind velocity of 5.0 m/s (Ibarra and Davalos, 1991) for Puerto Moreles, Q R. 

Wind transformity = 663 sej/J (Odum, 1996, p. 186) 

Diffusion coefficient - taken as similar to Tampa, Fl = 2.2 m3/m/sec (Odum, 1996, p.295) 

Vertical gradient - taken as similar to Tampa, Fl =1.9E-3 m/sec/m 

Kinetic energy of wind = (height) (density) (diffusion coefficient) (wind gradient) (area) 

energy at 1000 m = (1000 m) (1.23 kg/m3) (2.2 m3/m/sec) (5m/s/m) (lE6m2) 

energy = 1.35E12 J 

energy available at ground level = 20% (H.T. Odum, pers. comm ) = .2 * 1.35E10 J = 2.7E9 J 

6 HURRICANES 

Transformity = 9.579E4 sej/J (Scatena et al, in press) 

Method following that of Scatena et al. : 

average hurricane has kinetic energy of wind of 1 3E18 j/day (Riehl, 1979) 

assume has overall diameter of 500 km but hurricane winds in two 50 km zones around center, 

and strip 1 km wide passes over Akumal location; assume 10% of wind energy does work at surface 

assume area on average has major hurricane event every 50 years 



223 



Table 3-55 continued 



hurricane wind energy = (0.10)*(1.3 E18 J/day)* (0.25 days)* (1 km * (50+50 km)) / [(3.14*250*250 km)* 
(50yr)=1.14E13 J/yr 

7 WAVES 

Average wave height is given as 8 m for the coast at Puerto Moreles (Ibarra and Davalos, 1991) 
Energy of waves absorbed at shore = shore length* l/8*density*gravity*height squared * velocity (Odum 
1996, p. 298) 

velocity is: square root of gravity * depth at gauge (taken as 3 m for Akumal coastline)= 9.8m/sec2 * 

m A .5= 5.4m/sec 

energy = 1000 m * 1/8 * 1.025E3 kg/m3*9.8m/sec2 *.64 * 5.4m/sec = 4.34E6 

Transformity for wave energy = 25,889 sej/J (Odum, 1996) 

8 TIDE 

average tidal height of 18. 1 cm (Ibarra and Davalos, 1991) for Puerto Moreles, Q.R. 
transformity for tidal energy = 23,564 sej/J (Odum, 1996, p. 186) 

Energy = shelf area * (0.5) * tides/yr * (height squared) * (density) * gravity (Odum, 1996, p.298) 
=5E4m2 * 0.5 * 730 * 3E-2m2 * 1025 kg/m3 * 9.8 m/sec2 = 7.53 E5 

9. EARTH CYCLE 

Transformity = 29,000 sej/J (Odum, 1996, p. 186) 

Energy = (land area) (heat flow per area) 

heat flows for old stable areas is 1E6 j/m2/yr (Odum, 1996, p. 296) 

Energy = 1E6 m2 * 1E6 j/m2 = 1E12 

10 INLAND GROUNDWATER FLOW 

following methodology of Back, 1985: 

average rainfall = 1 .05 m - .9 m evapotranspiration = . 15 m mean annual recharge to groundwater 
area including inland drainage basin = 65,500 km2; total recharge = 9,800E6 m3 per yr. groundwater 
consumption (Lesser, 1976) is 350E6 m3/yr. Assuming this water is lost, total discharge along the 
approximately 1,100 km of coastline - 9450E6 m3/ 1 100 km = 8.6E6 m3/yr for each km of coastline 
the amount of groundwater underlying the coastal area can be estimated as around 3 m (Back, 1985) 
thus total groundwater in the study area is about 50% of this depth, or 1.5 m * 10E6 m2 = 1 5E7m3 
1.5E7 * 1000 kg/m3 * 4.94E3 J/kg = 7.41E13 

1 1 PUMPED GROUNDWATER 
calculated at 100 gallons/person/day 

Energy: 225 people *100gal/day * lm3/260 gallons * 365 days * 1000 kg/m3 * 4 94E3 J/kg 

Energy = 4.28E11 

Transformity = 4.8E4 (Odum, 1996, p. 120) 

12. LOSS OF SOIL (due to development) 

estimate loss of 20m2 of mangrove wetland per hotel * 4 = 80 m2 and 5 m2 per house * 1 5 = 60m2 

total 140 m2; depth of organic soil @ 0.3m * .06 g/cm3 (bulk density mangrove soil from this study) 

soil lost = 140 m2 * 0.3m * 1 E6cm3/m3 * 06g/cm3 = 2.52 E6 g in mangrove 

loss of soil of beach/sand dune ecosystems: 4 E3 m2 x 0.15m = 6 E2m3 * 1.0 g/cm3 (bulk density) 

soil lost = 6.2 E2m2 * 1 E6 cm3/m3 * 1 .0 g/cm3 = 6.2 E8g 

Energy = (2.52 E6g)*(0.76organic)*(5.4Kcal/g)*(4186J/Kcal) + (6.2 

E8g)*(0.03organic)*(5.4Kcal/g)*(4186J/Kcal) = 4.33 E9 J + 4.2E1 1 =4.24 El U 

Transformity = 7.37 E4 sej/J (Brown et al, 1992) 



224 



Table 3-55 continued 



13. LOSS OF VEGETATION (due to development) 

average biomass for mangrove = 15 kg/m2 (Mitsch and Gosselink, 1993); sand dune est. at 

0.5 = 7.5 kg/m2 

lost vegetation: 140m2 * 15 kg + 4 E3m2 * 7.5 kg = 3.21 E4 kg 

Energy = 3.21 E4kg * 1 E3 g/kg * 3.5 Kcal/g * 4186J/Kcal = 4.7 El 1 J 

Transformity = 2E5 (Brown et al, 1992 for agricultural. + forest products) 

14 LOCAL SERVICES 

estimated from revenues of local labor and businesses (e.g. diving shops, travel agency etc.) 
125 local workers @ $35 week * 52 weeks = $227,500 

15 higher paid labor (dive instructors, drivers etc.) @ $3,000/month * 12 = $540,000 
Total $7.68E5 

Mexican national sej/$ = 1.88 E12 (Trujillo, 1998) 

15 WOOD 

wood products harvested locally for construction, repairs + palm frond for roofing 

estimated at 500 m3/yr 

Energy = 500m3 * lE6cm3/m3 * 10176J/cm3 = 5.09E12 

transformity = 3.49E4 (Brown et al, 1992) 

16 LIMESTONE, GRAVEL, SAND 

limestone (+ local sand and gravel): used in construction and repair, 
from survey data: 120 m3/yr sand; 120 m3 gravel; 60 m3 limestone rock 

Transformity of limestone gravel and rock = 1.62E6 sej/J from Odum (1996, p. 310) 

Weight of limestone from Limestone Products, Newberry, FL (pers. comm): 3000 lbs/m3 

Energy (gravel) = 120 m3 * 3000 lbs/m3 * 454 g/lb *61 1 J/g = 9.99E10 

limestone rock, 5-10 cm. rock, from Limestone Products, Newberry, FL (pers. comm): 2700 lbs/m3 

Energy (rock)= 60 m3 * 2700 Ibs/m3 * 454 g/lb * 61 1 J/g = 4.49E10 

est. wt of sand from Florida Rock Mines, Grandin, FL plant (pers. comm): 3100 lbs/m3 

transformity of sand using Odum (1996, p. 310) for sandstone: 2E7 sej/J 

Energy (sand) = 120m3 * 3 100 lbs/m3 * 454 g/lb * 50J/g - 8.44E9 

total energy (gravel, rock and sand) = 1.53E11 

Composite transformity calculated by combining those for gravel, rock and sand in proportions of materials 
used 



17 FOOD 

Based on 2500 Kcal/person/day (10.47E6 J/day) and population on average of 225 

Transformity: 8.5E4 (Brown et al, 1992) 

Energy = 225 * 365 * 10.47E6J = 8.60E1 1 



18 GAS 

Hotel usage = 30,200 litters butane gas (survey data) * 6 = 181,200 1 butane/yr 

transformity = (Odum,. 1996, p. 187) 

Energy = 1.81E5 litters * 1 A3/28.3 litters * 1031 BTU/ft3 * 1055 J/BTU = 6.96E4 J 

19 FUEL (Petroleum products) 

Fuel usage by hotels (from survey data): 8500 litters gasoline/yr + 650 litters diesel 

if we combine gasoline+diesel, we can estimate that owner use of oil products is 9000 1 *6 = 54,000 1 



225 



Table 3-55 continued 



and adding 10 1/day *365 * 150 tourists = 547,500 litters/yr; total - 601,500 litters = 150,400 gal < 
54,000 gallons = 3008 barrels 

Oil products energy = 3008 barrels * 5.8E6 BTU/barrel * 1055 J/BTU - 1.84E13 
Transformity of petroleum products = 66,000 sej/J (Odum, 1996, p. 186) 

20 ELECTRICITY 

Transformity for electricity taken as mean global value = 173,681 sej/J (Odum, 1996, p. 305) 

Electrical usage: avg for hotels: 144,000 kWh/yr * 4 = 576,000 (from survey data) 

avg for homes: 5500 kWh/yr * 15 = 82,500 (from survey data) 
Energy = (658,500 kWh) * (3.606E6 j/kWh) = 2.37E12 J 



21 IMPORTED GOODS 

estimated as tourist revenues - local services - 25% profit on investment = 
1.96 E6$ - 7.68 E5$ - 4.9 E5$ = 7.02 E5$ 
Mexican national sej/$ = 1.88 E 12 (Trujillo, 1998) 

22 CAPITAL INVESTMENT 

capital investment, figured as $50,000 per house x 15 = $750,000 and $500,000 per hotel x4 = $2,000,000. 
Total $2,750,000 divided by lifetime of 20 years = $137,500 
Mexican national sej/$ = 1.88 E12 (Trujillo, 1998) 



23 TOURISM (Income) 

from survey data, $490,000/yr per hotel * 4 = $1,960,000 

To avoid double counting in table: tourist revenues - service - imported goods: 

1 .96 E6 - 7.02E5 - 7.68E5 = 4.9 E5$ 

Mexican national sej/$ = 1.88 E12 (Trujillo, 1998) 









226 




Figure 3-59 ; Systems diagram of the square kilometer coastal 
economy and environment, labelled with emergy flows from 
Table 3-57. 









227 



Table 3-56 Emergy indices for evaluating one square kilometer of developed coastline, 
Akumal, Mexico. 



Name of Index Definition One km 2 of developed coastline, 

Akumal, Mexico 

Nonrenewable/renewable F +N / R 1 .22 

Service /free S / N + R 0.32 

Empower density Emergy / area / time 1 .2 E 16 sej / ha / yr 

Emergy/$ ratio Emergy / money flow 5 . 7 E 1 2 sej/$ 

Investment ratio (F + S ) / (R+ N) 1 .49 



R = 4.77 El 8 sej/yr (Table 3-57, subtotal after line 11) 
N = 0.13 El 8 sej/yr (Table 3-57, subtotal after line 13) 
S = 1.57 E18 sej/yr (Table 3-57, lines 14 + 1/2 of line 22) 
F = 5.71 E18 sej/yr (Table 3-57, lines 15-23 - 1/2 of line 22) 
Empower density = 12.05 El 8 sej/yr / 100 ha = 1.2 E16 sej/ha/yr 



228 



$2.1E6(U.S.)/yr 




R = renewable 
resources 

N = non-renewable 
resources 

F = imported 
resourcs 

S = services 



Annual flows in 
E18 sej/yr 



Flow of $ 



Figure 3-60 Diagram of emergy and money flows in the 1 -square-kilometer 
coastal area, Akumal, Mexico. Units of diagram are expressed 
in El 8 sej (solar emergy joules)/yr. 






229 

5.7 E12 sej / $, four times greater than the U.S. and three times that of the national 
Mexican average (Trujillo, 1998), showing the dominance of environmental emergy flow 
vs. monetary flow in the region. 
Economic Evaluation 

The application of wetland treatment systems to the developed square 
kilometer will require the construction of wetlands to treat the hotels and houses. 
Construction costs vary depending on size of the wetland, with individual house systems 
being smaller and therefore more expensive than the research wetlands, and the hotel 
systems being larger and costing less. 

The two wetlands in our study averaged $165/person to construct. If we estimate 
the individual house systems as $250/person and hotels at $150/person, the costs for 15 
houses of 6 people each = $22,500 plus 4 hotels with 160 people - $24,000 for a total 
capital expenditure of $46,500. If lift pumps are required on half the systems (either 
because slopes do not permit gravity flow, or to get treated effluent to the receiving 
wetland), costs will be increased by around $3,000. Averaged over 20-year lifetime (and 
5 years for pumps), this equals $2,925/yr. Maintenance costs are estimated at $100 per 
house system, $500 per hotel system, for a total of $3500/yr. Total yearly expenditures 
are thus $6,425 for the wetland treatment units to serve the developed square kilometer. 

Package plants would cost $15,600 for each of the hotels and if the houses send 
their sewage to a common collection point, the equivalent of 2.25 additional package 
plants will be required. Additional pumping/piping to centralize the house sewage will 
add an additional $10,000. The overall capital cost will be $107,500, and with an 



230 

average lifetime of 7.5 years (averaging machinery and other components) is $14,330/yr. 
Maintenance costs at $1 100/system will be $6,875, so total costs are $21,205/yr. 

Given a yearly money flow of about $1,950,000 for the developed kilometer 
in Akumal, capital and operating/maintenance (O/M) costs of the wetland treatment 
systems equals 0.3% of this economic activity, and capital and O/M costs of the package 
plants would account for 1.1% of overall monetary flows. 

Electricity required for the package plants are estimated at 250 Kilowatt-hours 
(kWh)/month/system or 18,750 kWh/year for the 6.25 package plants in the coastal area. 
This is 2.8% of the total electrical usage of the developed kilometer. Should half the 
wetland treatment systems require use of a submersible lift-pump, electrical usage will be 
around 35 kWh/month or 420 kWh/yr, so 10 pumps will use 4,200 kWh, or 0.6% of total 
electrical usage of the developed square kilometer. 
Water Budget 

Water budgets for a square kilometer of coastline were prepared for the square 
kilometer development scenario with no sewage treatment and the changes to the water 
budget assuming that all human wastewater is treated by the installation of wetland 
systems (Table 3-57, Figure 3-61). 

These regional water budgets show that the largest water inputs are from tidal 
exchange (36.5E6 m3/yr) and secondly from inland groundwater (8.6E6 m3/yr). These 
quantities of water far exceed that of pumped groundwater used by the area's population 
(1.7E4 m3/yr). However, pumped groundwater is far larger than the quantity of water 
deriving from precipitation that directly falls on the square kilometer (1.05E3 m3/yr). 



231 






Table 3-57 Water budget of a square kilometer of coastline around research site without 
use of wetland treatment systems. Changes with use of wetland treatment units are shown 
in parentheses. 



Item 



Water in: 

1 Direct precipitation 

2 Pumped groundwater used by people 

3 Inland groundwater flow 

4 Tidal inputs 
Total water in 



Quantity of water m /yr 
E5 m 3 /yr 



0.01 

0.17 

86 

365 

451.2 



Water out: 
5 ET 



Subsurface groundwater discharge to sea (includes tidal 
return + discharge of input precipitation, domestic 
sewage + inland groundwater) 

Total water out 



8.59 
(+0.02) 

442.6 
(-0.02) 



451.2 



Notes: 



1 Precipitation 

Based on average precipitation of 1050 mm for Yucatan (Lesser 1976) 
1.05* 1000 m 2 = 1050 m 3 

2 Pumped groundwater use 

based on estimated population of 250 people x 50 gallons/person/day 
250 * 50 gallons * 365 - 4.56E6 gal/yr * m 3 /264 gal = 17,280 m 3 



3 Inland groundwater flow 

based on estimate (Back, 1985) on average discharge of groundwater per km of coastline 

in northeastern Yucatan 



232 

Table 3-57 continued 

4 Tidal exchange 

~ estimated on basis that 1 m of saltwater underlies and mixes with freshwater: 1000m * 
1000m * 1 m = lE6m and that turnover is every 10 days 
365/10 = 36.5/yr * lE6m 3 = 36.5E6m 3 /yr 

5 Evapotranspiration 

sum of 

a. estimates by Lesser (1976) that .9 m on average of 1.05 of precipitation was 
evapotranspired in the Yucatan 

.9m* 1 000m 2 = 900 m 3 

b. plus 690 m from ET of water used for watering gardens etc. 

(based on estimates that average per capita production of wastewater is 30 gal/person/day 
in the Yucatan. 20 gal/person/day is the difference between water consumption and 
wastewater production rates, usually largely accounted for by watering of gardens etc. 
assume that this water has same characteristics as GW pumped 
20 gal/person/day * 250 people * 365 * m 3 /264 gal = 6,910 m 3 
further assume that 10% of this water is lost to ET before infiltrating 
therefore, ET is increased by 690 m 3 ) 

c. plus water evapotranspired by mangrove wetlands of area 

based on water budget for southern Florida mangrove swamp (Twilley, 1982) - 108 
cm/yr, so if mangrove + other natural wetland vegetation covers 50 ha (half) of area = 
50*10,000 m 2 * 1.08m = 5.4E5 m 3 . 

Total ET = 9 E2 + 6.9 E2 + 8.57 E5 = 8.59 E5 m 3 



Impact of wetland based on wastewater discharge of 30 gal/person/day estimate. 
30 gal/per person/day * 250 people * 365 day/yr * m 3 /264 gal - 10,370 m 3 
However, with use of wetlands, estimated ET losses of wastewater 
are 20% (from research for this study) 
therefore ET is increased by 2, 070 or 0.02E5 m 3 

6 Subsurface discharge is based then on difference between inputs and ET since there 
is no surface water discharge. 



233 



.Precipitation 

0.01 



86 

Inland 

groundwater 

low 




0.17 



Pumped 



Evapotranspiration 
8.59 
(+0.02 =8.61) 




One square kilometer 
developed coastline 
Akumal, Mexico 



water flows E5 m 3 /yr 



groundwater 



Tidal input 
365 E5 




+ 442.6 E5 
Subsurface discharge (-0.02 = 442.58) 
to the sea 



Figure 3-6 1 Diagram of water budget of one square kilometer of 
developed coastline, Akumal, Mexico. Figures in parentheses show changes 
in budget if all sewage is treated by constructed limestone wetlands. 



234 

The regional water budget with installation of wetlands for treatment of all wastewater 
shows a higher percentage of water going to ET, as occurs currently as the ET is greatly 
increased by the estimated 20% evapotranspiration of sewage influent to the wetlands 
(Table 3-57). . 
Nutrient Budget 

Table 3-58 shows the quantities of nitrogen, phosphorus, organic compounds 
(BOD) and coliform bacteria added to the groundwater of the square kilometer if 
development occurs without sewage treatment and if wetland systems are used. Use of 
the wetland treatment systems for the 250 people living in the square kilometer area 
results in reductions of 76% for N added to the groundwater, 85% less P being added, 
88% less BOD (organic compounds) and 99.97% less fecal coliform bacteria being added 
(Table 3-58). These reductions amount to 75 kg less P, 425 kg less N, and 1430 kg less 
BOD in the groundwater on an annual basis. When the further uptake and retention in the 
receiving mangrove wetlands are included, discharge of N,P, BOD and coliform are 
further reduced. 

It is more difficult to estimate what levels of nutrients and coliform bacteria will 
be discharged to the sea from our study area. Some nutrients are undoubtedly utilized by 
soil bacteria and vegetation in the coastal wetlands and beach zone, and some nitrogen 
are volatilized due to oxidative/reductive biochemical reactions in wetland zones. Some 
phosphorus may be absorbed in limestone in the subsurface zone. Coliform bacteria have 
an extinction rate in inhospitable environments, apart from other processes such as plant 
and bacterial antibiotics which lower their number. The budgets for phosphorus, 



235 



Table 3-58 Comparative additions to groundwater (GW) of nitrogen, phosphorus, BOD 
(organic compounds) and fecal coliform from domestic sewage in a 1 -square-kilometer 
area of study site with and without the use of wetland treatment systems. 



Item 


Addition to GW 


Addition to GW 


Reduction in kg 


Percent 




without use 


of 


with use of 


(or number of 


reduction by 




wetlands 




wetlands 


bacteria) 


use of wetlands 












+ mangroves 


Nitrogen 


466.7 




41.5 


425.2 kg 


91% 


Phosphorus 


83 kg 




8.3 kg 


74.7 kg 


90% 


BOD 


1504 kg 




75 kg 


1429 kg 


95% 


Fecal 


1.04 E14 




0.001 E14 


1.039 E14 


99.99+% 


coliform 


bacteria 




bacteria 


bacteria 





Notes: 

wastewater infiltration based on 30 gal/person/day estimate. 

30 gal/per pers./day * 250 people * 365 day/yr * m 3 /264 gal = 10,370 m 3 

With use of wetlands, estimated ET losses of wastewater are 20% (from research for this study) therefore 

ET is increased by 2, 070 m 3 and wastewater infiltration is 8,300 m 3 

N based on average input levels of 45 mg/1 and discharge levels of 10 mg/1 in wetland system effluent 

(from this research study) 

45 mg/1 * 1000 1/m 3 * 10,370 m 3 * kg/E6 mg = 466.7 kg 

10 mg/1 * 1000 1/m 3 * 8,300 m 3 * kg/E6 mg = 83 kg - 50% reduction in mangroves = 41 .5 kg 

P based on average input levels of 8 mg/1 and discharge of 1 6 mg/1 in wetland system effluent (from this 
research study) 

8 mg/1 * * 1000 1/m 3 * 10,370 m 3 * kg/E6 mg = 83 kg 

80% reduction in wetlands + 50% in mangroves = discharge of 8.3 kg P (reduction of 74.7 kg P) 

BOD based on average input of 145 mg BOD/kg and discharge of 18 mg/1 in wetland system effluent (from 

this research study) 

145 mg/1 * 1000 1/m 3 * 10,370 m 3 * kg/E6 mg = 1504 kg BOD 

18 mg/1 * 1000 1/m 3 * 8,300 m 3 * kg/1000 mg = 149 kg + 50% reduction in mangroves = 75 kg 

Coliform numbers based on influent of 1E6 per 100 ml (1E7 per liter) and discharge of 2000 per 100 ml 

(2E4 per liter) in wetland system effluent (from this research study) 

1E7/Iiter * 1000 1/m 3 * 10,370 m 3 = 1.04 E14 coliform 

2E4/liter * 1000 1/m 3 * 8,300 m 3 = 1.66E1 1 coliform (0.001 E14) 



236 

nitrogen, organic materials (BOD) and coliform inputs, are shown in Tables 3-59, 3-60, 
3-61 and 3-62 and are diagrammed in Figures 3-62, 3-63, 3-64 and 3-65. These regional 
budgets indicate that for a population of 250 people along 1 square kilometer of 
developed Yucatan coastlines, the use of the wetland treatment units will reduce yearly 
discharge to the sea of around 680 kg of organic matter (BOD), 190 kg of nitrogen, 50 kg 
of phosphorus and reduce total coliform discharge by over IE 13 coliform bacteria. 




























237 



Table 3-59 Phosphorus budget of a developed square kilometer of coastline, Akumal, 
Mexico with no sewage treatment and changes if wetland systems are installed. 





Item 


Quantity of 
water m/yr 


Quantity of P 
kg P/yr 


Change if wetland 
treatment systems 
used 

kg P /yr 


1 


Inputs to system: 
In water: 
precipitation 


1.05 E3 


neg. 




2 


pumped GW 
used by people 


1.728 E4 


0.5 




3 


Inland groundwater flow 


8.6E6 


258 




4 


Tidal exchange 


36.5E6 


3.7 




5 


In solids: 
Food 
Total in 




83.0 

345.2 






45.123 E6 




6 


Inside system: 
Addition to groundwater 
from domestic sewage 


1.037 E4 


83.0 


8.3 

(difference is -74.7) 


7 


Increase in storage: 
limestone + 
vegetative/bacteria 
biomass 




86.3 


140.3 
(difference is +54) 



Outputs from system: 

8 ET 

9 Subsurface groundwater 
discharge to sea 



8.59 E5 
44.26441 E6 



Negligible. 
258.9 



Negligible. 
204.9 

(difference = -54) 



Notes: 

(see also notes to Table 3-50 and 3-52) 



based on estimated population of 250 people x 50 gallons/person/day 
250 * 50 gallons * 365 = 4.56 E6 gal/yr * m 3 /264 gal = 17,280 m 3 
P content based on average of 15 groundwater samples collected by C. Shaw and M. 
Nelson 12 Jan 97 and analyzed at the labs of the Soils Dept. Univ. of Florida, which 



238 

Table 3-59 continued 

hadavgPof0.03mg/l. 

P = 0.03 mg/1 * 1000 1/m 3 * 1.728 E4 m 3 * kg/1 E6 mg - 0.52 kg P 

3 

based on estimate (Back, 1985) on average discharge of groundwater per km of coastline 

in northeastern Yucatan 

P = 0.03 mg/1 * 1000 l/m3 * 8.6 E6m3 * kg/1 E6 mg = 258 kg P 

4 

tidal exchange ~ estimated on basis that 1 m of saltwater underlies and mixes with 

freshwater: 1000m * 1000m * 1 m = lE6m3 and that turnover is every 10 days 

365/10 = 36.5/yr * lE6m3 = 36.5E6m3/yr 

P concentration in seawater (Drever, 1988) averages 0.001 mg/kg 

total P - 36.5E6m3 * 0.001 mg/kg * kg/lE6mg * 1.025E3kg/m3 - 3.7 kg 

5 

food P matches approx. discharged P in sewage (see note 6) 

6 

wastewater infiltration based on 30 gal/person/day estimate. 

30 gal/per pers./day * 250 people * 365 day/yr * m 3 /264 gal = 10,370 m 3 

P based on average levels of 8 mg/1 in septic tank effluent (from this research study) 

8 mg/1 * 1000 1/m 3 * 10,370 m 3 * kg/E6 mg = 83 kg 

addition to groundwater = 75% x 83 = 62.3 (w/o wetland sewage treatment) 

Reduction in wetland treatment systems: 80% in wetlands (from this study) + 50% in 

mangrove (est.) 

83 * .2 = 16.6 * .5 = 8.3 kg P added to groundwater with sewage treatment (a reduction 

of 74.3 kg) 

7 

if no sewage treatment, estimate storage in limestone + vegetative/bacterial biomass = 

25% of P in groundwater from sewage additions and natural inputs) 345.2 * 0.25 = 86.3 

wetland + mangrove sewage treatment removes 74.7 kg P of wastewater P, and natural 

removal 

is 25% of 262.2 kg P (other inputs of P) = 65.55; total storage = 56.1 + 65.55 =140.3 kg P 

9 

if assume in scenario of development without sewage treatment that uptake of P by 
limestone and bacteria/vegetation is 25%, P is reduced from (6.222 E4 + 5.24 E2 = 6.274 
E4)/4 = 4.71E4 

in scenario of wetland treatment systems, P is further reduced by mangrove receiving 
wetlands (data forthcoming from ongoing research). If reduction is 90%, then P reduces 
from (9.13 E3 + 5.24 E2 = 9.654 E3) * (0.1) = 9.65 E2 



239 



Food 



a/ Phosphorus budget without sewage treatment 



83 



Tide + 

Inland groundwater 

+ pumped water 

262.2 



One square kilometer 
developed coastline 
Akumal, Mexico 



Addition to 
groundwater 
.frorr^ sewage 

83 



Phosphorus flow kg/yr 




Food 



Tide + 
inland GW 
+ pumped 
water 

'62.2 



b/ Phosphorus budget with constructed limestone 
wetland treatment systems + receiving wetlands 




83 



One square kilometer 
developed coastline 
Akumal, Mexico 




Phosphorus flow kg/yr 



Addition to 
groundwater 
_from sewage 

8.3 

(-74.7) 



Subsurface 
discharge 
to sea 

258.9 



Subsurface 
discharge 
to sea 

204.9 
(-54) 



Figure 3-62 Diagram of phosphorus budget of one square kilometer of 

tSSSSXl Akuma1 ' ^ ex,co F,gures in parentheses show ch -g- 
£*£ weir 86 1S treated by constmcted ,imestone wet,ands - 



240 



Table 3-60 Nitrogen budget of a developed square kilometer of coastline, Akumal, 
Mexico with no sewage treatment and changes if wetland systems are installed. 



Item 


Quantity of 
water m 3 /yr 


Quantity of N 

kg N/yr 


Change if wetland 
treatment systems used 

kg N/yr 


Inputs to system: 
In water: 
1 Precipitation 


1.05 E3 


786 




2 Pumped GW 
Used by people 


1.728 E4 


19.5 




3 Inland groundwater flow 


8.6 E6 


9720 




4 Tidal exchange 


36.5 E6 


18.7 




Subtotal (water inputs) 


45.123 E6 


10,526 




5 In solids: 




467 




Total In 




10,993 




Inside system: 









6 Addition to groundwater 1.037 E4 467 
from domestic sewage 

7 Increase in storage 2748 
within system 

Outputs from system: 



41.5 

(difference = -425.5) 

3045 

(difference = +297) 



8 ET 



8.5859 E5 



Neg. 



9 Subsurface groundwater 44.26441 E6 5,492 
discharge to sea 



Neg. 

5,305 
(difference 



187) 



Notes: 

(see also notes to Table 3-65 and Table 3-67) 



1 Based on average precipitation 
1.05* 1000 m r = 1050 m 3 



of 1050 mm for Yucatan (Lesser, 1976). 



241 

Table 3-60 continued 

N-content of precipitation based on Valiela and Teal (1979) in their N budget for a Cape 
Cod salt marsh concluded rainfall contributed 0.786 gN/m 2 /yr or 7.86 kg N/ha/yr. There 
are 100 hectares in 1 km 2 , hence: 7.86 kg * 100 = 786 kg 

2 based on estimated population of 250 people x 50 gallons/person/day 
250 * 50 gallons * 365 = 4.56E6 gal/yr * m 3 /264 gal - 17,280 m 3 
N content based on average of 15 groundwater samples collected by C. Shaw and M. 

Nelson 12 Jan 97 and analyzed at the labs of the Soils Dept. Univ. of Florida, which 

had avg N of 1.13 mg/1. 

N = 1.13 mg/1 * 1000 1/m 3 * 1.728E4 m 3 * kg/lE6 mg= 19.5 kgN 



3 based on estimate (Back, 1985) on average discharge of groundwater per km of 
coastline in northeastern Yucatan 

N= 1.13 mg/1 * 1000 l/m3 * 8.6E6m3 * kg/lE6 mg - 9,720 kg N 

4 tidal exchange ~ estimated on basis that 1 m of saltwater underlies and mixes with 
freshwater: 1000m * 1000m * 1 m = lE6m3 and that turnover is every 10 days 
365/10 = 36.5/yr * lE6m3 = 36.5E6m3/yr 

N concentration in seawater (Drever, 1988) averages 0.005 mg/kg 

total N = 36.5E6m3 * 0.005 mg/kg * kg/lE6mg * 1 .025E3kg/m3 = 18.7 kg 

5 Food inputs of N taken to be equal to sewage-content of N 

6 wastewater infiltration based on 30 gal/person/day estimate. 

30 gal/per pers./day * 250 people * 365 day/yr * m7264 gal = 10,370 m 3 

N based on average levels of 45 mg/1 in septic tank effluent (from this research study) 

45 mg/1 * 1000 1/m 3 * 10,370 m 3 * kg/E6 mg = 466.7 kg 

with wetland treatment: 10 mg N/1 * 1000 1/m 3 * 8300 m 3 * kg/E6 mg = 83 kg * 50% 

reduction in mangrove: 41.5 kg 

7 storage w/o treatment based on 25% uptake of N (see note 9): 2748 kg 

storage with treatment: 25% of 10526 kg N = 2631.5 + 50% of 425.5 kg N reduction of 
sewage: 413 = 3045 kg N 

9 without sewage treatment: if 50% of input N (10,993) is either volatilized as N2 gas or 
taken up by sediments, bacteria and vegetation in the coastal zone, then 5,492 kg will be 
released to the sea in subsurface flow 

wetland systems with further treatment in receiving wetland: discharge = .5 x 10,526 = 
5263 + 41.5 from sewage = 5,305 kg 



242 



Food 



a/ Nitrogen budget without sewage treatment 
467 "N 



Tide+ 
inland GW 
+pumped 
water 



10.526 



/ 


One square kilometer 
developed coastline 
Akumal, Mexico 


Subsurface 
discharge 




/^Addition to \ 


to sea 




( groundwater 
\fa>m sewage 


5,492 




467 




\ 


Nitrogen kg N/yr 





Food 



b/ Nitrogen budget with constructed limestone 
wetland treatment systems + receiving wetlands 



467 



^\ 



Tide+ 
inland GW 
+pumped 
water 



10.526 



One square kilometer 
developed coastline 
Akumal, Mexico 



Addition to 
groundwater 
from sewage 



Nitrogen kg N/yr 



Subsurface 
discharge 
to sea 

5,305 
(-187) 



Figure 3-63 Diagram of nitrogen budget of one square kilometer of 
developed coastline, Akumal, Mexico. Figures in parentheses show 
changes in budget .fall sewage is treated by constructed limestone 
wetlands and receiving wetlands. 









243 



Table 3-61 Organic compounds (BOD) budget of a developed square kilometer of 
coastline, Akumal, Mexico, with no sewage treatment and changes if wetland systems are 
installed. 





Item 


Quantity of 
water m 3 /yr 


BOD 
kg/yr 


Changes if wetland 
systems are used 
kg BOD/yr 


1 

2 

3 
4 

5 

6 

7 


Inputs to system: 
In water: 
Precipitation 

pumped G W 

used by people 

Inland groundwater flow 

Tidal exchange 

Subtotal in (water 

inputs) 

In solids: 

Food 

Total in 
Inside system: 
Addition to groundwater 
from domestic sewage 

Increases in storage in 
the system 


1.05 E3 
1.728 E4 

8.6 E6 
36.5 E6 
45.123 E6 


neg. 

neg. 

neg. 
neg. 
neg. 

1504 
1504 
1504 

752 




1.037 E4 


75 

(difference is 1429 kg 

BOD) 

1479 









Outputs from system: 
8 ET 



8.5859 E5 



9 Subsurface groundwater 
discharge to sea 



44.26441 E6 752 



75 

(difference is 677 kg 

BOD) 



Notes: 

(see also notes to Table 3-65 and Table 3-67) 

6 

wastewater infiltration based on 30 gal/person/day estimate. 

30 gal/per pers./day * 250 people * 365 day/yr * m 3 /264 gal = 10,370 m 3 

BOD based on average input of 145 mg BOD/kg and discharge of 18 mg/1 in wetland system effluent (from 

this research study) 

145 mg/1 * 1000 1/m 3 * 10,370 m 3 * kg/E6 mg = 1504 kg BOD 

18 mg/1 * 1000 1/m 3 * 8,300 m 3 * kg/1000 mg = 149 kg + 50% reduction in mangroves = 75 kg 



9 discharge to sea: 

if 50% of BOD is removed in groundwater: 752 stored in biota 



244 



a/ Organic matter (BOD) budget without sewage treatment 



Food 



1504 

Tide + 
inland GW 
+pumped 
water 

negl. 



One square kilometer 
developed coastline 
Akumal, Mexico 



Addition to 
groundwater 
from sewage 

1504 



BOD kg BOD/yr 



Subsurface 
discharge 
to sea 

752 



b/ Organic matter (BOD) budget with constructed limestone 
wetland treatment systems + receiving wetlands 



Food 



Tide + 
inland GW 
+pumped 
water 



negl. 



One square kilometer 
developed coastline 
Akumal, Mexico 



'Addition to 
groundwater 
(rom sewage 

75 

(-677) 



BOD kg BOD/yr 



Subsurface 
discharge 
to sea 

75 
(-677) 



Figure 3-64 Diagram of organic matter (BOD) budget of one square 
kilometer of developed coastline, Akumal, Mexico. Figures in parentheses 
show changes in budget if all sewage is treated by constructed limestone 
wetlands and receiving wetlands. 



245 









Table 3-62 Coliform bacteria budget of a developed square kilometer of coastline, 
Akumal, Mexico, with no sewage treatment and changes if wetland systems are installed. 





Item Quantity of 

water m 3 /yr 


# of fecal 
coliform 


Changes if wetland 
systems are used 
# of fecal coliform 


1 


Inputs to system: 

Precipitation 1.05 E3 


neg. 




2 


Pumped GW 1.728 E4 
used by people 


neg. 




3 


Inland groundwater 8.6 E6 
flow 


neg. 




4 


Tidal exchange 36.5 E6 


neg. 






Total in 45.123 E6 


neg. 




5 


Inside system: 

Addition to 1.037 E4 

groundwater from 

domestic sewage 


1.04 E14 


0.001 E14 
(difference = 
-1.039 E14) 


6 
7 


Outputs from system: 

ET 8.5859 E5 

Subsurface 44.26441 E6 

groundwater 

discharge to sea 


1.04 E13 


0.005 E13 
(difference = 
- 1.035 E13 
coliform) 


Notes: 

(see also notes to Table 3-50 and Table 3-52) 







wastewater infiltration based on 30 gal/person/day estimate. 

30 gal/per pers./day * 250 people * 365 day/yr * m 3 /264 gal = 10,370 m 3 

Coliform numbers based on influent of 1E6 per 100 ml (1E7 per liter) and discharge of 2000 per 100 ml 

(2E4 per liter) in wetland system effluent (from this research study) 

1E7/Iiter * 1000 1/m 3 * 10,370 m 3 = 1.04 E14 coliform 

2E4/liter * 1000 1/m 3 * 8,300 m 3 = 1.66E11 coliform (0.001 E14) 



without sewage treatment: if coliform are reduced 90% before discharge to sea 
= 1.04E14*.l = 1.04E13 

with wetland treatment systems: if receiving wetlands further reduce coliform 
by 50%, then discharge water will contain 0.01E13 * .5 = 0.005E13 






246 



a/ Coliform bacteria budget without sewage treatment 





f " " 




One square kilometer 


Tide + 


developed coastline 


inland GW 


Akumal, Mexico 


+pumped 




water 


s^ Addition in 


\negl. 


f sewage 


X^ 


V disposal 


*" 


" ^ 1.04 E14 




Coliform bacteria # 



Subsurface 
discharge 
to sea 
1.04 E13 



b/ Coliform bacteria budget with constructed limestone 
wetland treatment systems + receiving wetlands 



Tide + 
inland GW 
+pumped 
water 
Jiegl. 



One square kilometer 
developed coastline 
Akumal, Mexico 




Coliform bacteria # 



Addition in 

sewage 

disposal 
0.001 E14 
(-1.039 E14) 



Subsurface 
discharge 
to sea 
0.005 E13 
(-1.035E13) 



Figure 3-65 Diagram of coliform bacteria budget of one square kilometer 
of developed coastline, Akumal, Mexico. Figures in parentheses show 
changes in budget if all sewage is treated by constructed limestone 
wetlands and receiving wetlands. 



CHAPTER 4 
DISCUSSION 

Contribution of Research to Science of Ecological Engineering 

The principal contributions of the present research to the science of ecological 
engineering are in its use of local limestone gravel as substrate for the wetland, the 
demonstration that high species diversity can be maintained from the outset in a 
constructed wetland, and its successful integration in the regional environment by the use 
of mangrove wetlands as the final bio-filter for the treated wastewater. 

Limestone proved to be effective in improving phosphorus treatment by the 
wetlands (Figure 3-39 and Figure 3-40). Since limestone is a local Yucatan material, it 
also was important in lowering cost of construction and increasing the use of regional 
natural resources compared to alternative, conventional sewage treatment systems. 

Although the research aimed at high diversity, it was unexpected that the 
wetlands would substantially increase and sustain plant species beyond the 35 planted 
(Table 3-1), demonstrating that species from the local environment were able to 
successfully invade and contribute to the ecosystem. This runs counter to current practice 
in constructed wetlands for sewage treatment where few species are planted, and almost 
all of which tend to be dominated by aggressive pioneer species of wetland bulrush, reed 
and cattail. 



247 



248 

The use of mangroves as a final bio-filter and recipient of the effluent from the 
limestone wetlands may be an important advance in ecologically engineering, for usually 
constructed wetlands are placed into environmental contexts with little regard for their 
integration in the larger ecological system. In coastal Yucatan, the mangroves are the 
natural interface between the human economy and the beach/marine zone and offer great 
advantages in that they have an organic sediment which can function as a biotic filter for 
groundwater flow of nutrients. This type of mangrove use should increase awareness of 
the importance of the mangroves in maintaining environmental health in the region and 
offer cogent reasons to prevent their continued destruction for tourist development. 

The wetlands have also been shown to be less costly in construction and operation 
than conventional sewage treatment (Tables 3-34 and 3-35). The limestone wetlands also 
use far more local resources and less imported goods and services (Tables 3-36 and 3- 
37). Both these factors facilitate their practical application for third world tropical 
countries where capital and technical expertise is limited. 

Analysis of the regional nutrient budgets show that the wetlands would prevent 
virtually all anthropogenic nutrients from entering the groundwater and impacting coastal 
ecosystems (Tables 3-59 to 3-62). This type of ecologically engineered system may help 
ensure the health of regional ecosystems normally put at risk by tourist development. 

Ecological Succession in the Limestone Wetland Units 

The Akumal limestone wetlands have demonstrated a rapid pattern of ecological 
succession. In August 1996 the wetlands were first planted, and initially had only partial 
cover of the ground, little canopy structure, and an average height of 0.5 m. The wetlands 



249 

were not connected to sewage flow until December, 1996, and during that period 
demonstrated little growth. Once sewage flow commenced, plant growth and canopy 
development were quite rapid as ecological succession theory would suggest. By May 
1997 when the first extensive surveys were conducted, the dominant plants were Carina 
edulis, Nerium oleander, Typha domingensis and Alocasia esculenta, and average height 
had increased to lm. By December 1997 and July 1998, the increasing prominence of 
upper canopy trees and palms was evident. Lower canopy vegetation remained, but the 
system now favored shade-tolerant species. Lower canopy and annual species were the 
most likely species to be lost from the system. By July 1998, canopy closure averaged 
85% in the wetlands (Table 3-15), light interception was around 90% (Table 3-14), and 
average plant height was around 2 m (with some of the top canopy reaching 4-5 m). 

It appears that the wetlands are still in early succession. On each of the last two 
surveys (December 1997 and July 1998), about 20% of previous species were lost, and 
were replaced by new species. Some of the differences in development may be the result 
of stochastic processes, and even from the random choice of which plants were placed in 
the different cells. While the striking difference in plant development and leaf area index 
between first and second cells has been eliminated in Wetland System 2, there is still a 
marked difference in Wetland System 1 (Table 3-11). 

Odum (1994) notes that the equalization of productivity and respiration seen in 
the later stages of many successions may not apply in situation where ecosystems receive 
a continued input of nutrients and convert it into organic storage, as in a sewage 
treatment wetland. Detritus flushed into mangroves is likely to be beneficial. Currently, 



250 

plant growth and canopy development still continues, and may be expected to do so until 
trees and palms attain their full height. 

Succession theory predicts that organic matter will build in the ecosystem (Odum, 
1971), a result not seen in the two years since construction (Figure 3-26). However, the 
original sawdust mulch has been replaced by litterfall, and as biomass continues to 
increase, one would expect the quantity of litterfall will increase. 

Animal usage of the wetlands was not monitored in this research, but it was noted 
that frogs invaded the wetlands within months of its creation. Snake skins have been 
found in the system and birds have been observed in the system. Dozens of insects were 
observed during the studies of leaf holes (Tables 3-12 and 3-13) on the plants, evidence 
of active herbivory. 

Figure 3-45 summarizes the main processes in the ecosystem during its first two 
years including the inputs and transpiration of water, the production and deposition of 
organic matter, the absorption of nutrients and possible role of salt in maintaining 
biodiversity. 

Comparison of the Akumal Systems with other Treatment Approaches 

The Akumal wetlands are low in cost, and low in requirements for imported 
goods and electricity as are other low-tech approaches such as use of surface flow 
wetlands and aerated lagoons. However, aerated lagoons and surface flow wetlands may 
not be suitable for use in the Yucatan unless built with impermeable liners, as otherwise 
wastewater will be lost to the permeable limestone before adequate treatment is effected. 



251 

Conventional sewage treatment plants are very capital-intensive. Three-quarters 
of overall costs are involved in the pumping required to move raw sewage to the 
centralized sewage plant (Southwest Wetland Group, 1995). Much of the cost for 
conventional sewage treatment is for purchased goods, which originates outside the 
region and frequently is imported in third world countries. Operation and maintenance 
costs are high, since such facilities require highly trained technicians and engineers. For 
example, the University of Florida wastewater treatment facility has capital costs over 
three times higher per person than the Akumal wetlands, and operating costs at 
$27/person/year are nine times higher (Appendix D, Table 3-36) 

Electrical costs are high for conventional sewage treatment plants since much of 
the system process relies on machinery. Maintenance for such systems can be expected 
to be more expensive in the Yucatan because of the tropical environment, salt-spray and 
saline groundwater, and the high cost of importing equipment from elsewhere in Mexico 
or the United States. Treatment by package plants decreases over time with poor 
maintenance of equipment and inadequate technical supervision (Reed et. al., 1995). 

In addition, conventional treatment systems and package plants are designed to 
achieve secondary treatment standards (<30 mg/1 of biochemical oxygen demand and 
total suspended solids) which may be inadequate for preventing eutrophication of marine 
and terrestrial environments. Large amounts of sludge are produced, which are difficult 
in an environment like the Yucatan to dispose/use in a responsible manner. For example, 
the sewage treatment system for the city of Cancun, Quintana Roo has contributed to 
pollution of the Cancun lagoon. 



252 

Shallow-well injection following septic tank residence is low cost, but not very 
effective in reduction of organic compounds, nutrients or coliform bacteria or in 
preventing their impact on sensitive coastal marine ecosystems. Septic tank residence, 
with adequate holding time, only reduces influent BOD <50% (TVA, 1993). Wastes in 
partially treated wastewater are likely to accumulate in the groundwater and coastal 
waters of the Yucatan. In similar geological setting, in the Florida Keys, sewage injected 
into shallow wells on land was found less than one mile away in off-shore waters (Shinn 
etal, 1992). 

Aquatic plant treatment systems (Wolverton, 1987) and surface flow wetlands 
have the advantages of being low cost to build and operate, and have been applied in 
many ecosystems and climatic zones, using locally available wetland species. They often 
are designed for secondary/tertiary wastewater treatment, with lagoons or other settling 
devices accomplishing primary treatment before release of the wastewater. 

However, surface flow wetlands require more area than subsurface wetlands. This 
is because subsurface flow wetlands are designed to make the wastewater flow through 
the entire volume of their gravel substrate, as contrasted with surface flow wetlands 
where wastewater flows over the top of the soil bed. Thus the surface area of each piece 
of gravel in a subsurface system can function as a locale for hosting microorganisms and 
as a site for wastewater filtration, sedimentation and microbial interaction. A rule of 
thumb is that surface flow wetlands require about 100 hectares (250 acres) for treatment 
of 1 -million gallons/day wastewater loading vs. 5-10 hectares (12-25 acres) for 
subsurface flow wetlands, such as were used in Akumal (Kadlec and Knight, 1996). 



253 

The cost of the medium (generally gravel) and liners usually makes the cost per 
area more for constructing subsurface flow wetlands, but this is offset by the smaller area 
and heavier loading that such systems receive. Thus subsurface wetlands are usually less 
expensive than aquatic plant systems or surface flow wetlands (TVA, 1993, Reed et al., 
1995). For these reasons, and because such systems would need to be lined if applied in 
the Yucatan, there is probably limited scope for the use of surface flow wetlands for 
wastewater treatment in the region. Aquatic plant constructed wetlands may also 
generally require biomass harvesting (Bagnall et al, 1993), which requires additional 
labor and is seldom cost-effective (Reed et al, 1995). 

There may be applications where use of several approaches can be usefully 
combined. For example, in some constructed wetland systems, ponds have been used 
rather than septic tanks as the primary treatment stage to reduce construction costs. 
Wetlands have also been used following conventional treatment or package plants to 
increase nutrient recycling and produce higher quality effluent water. 

There are numerous natural freshwater and saltwater wetlands that occur in the 
coastal zone of the Yucatan. Environmental protection regulations in the U.S. have made 
it more difficult to obtain permits for the use of natural wetlands for sewage treatment or 
disposal, despite the fact that there are numerous examples of successful historical and 
recent use of natural wetlands for this purpose. 

In the Yucatan the relatively open hydrology of wetlands, due to the limestone 
geology and rapid movement of water into and through the underlying limestone, 
cautions against the use of natural wetlands as a primary mechanism of sewage 
treatment. However, these wetlands are the only coastal ecosystems with a substantial 



organic soil component, and as such they function as natural bio-filters. Perhaps the most 
appropriate use of such wetlands is as a final step in sewage treatment, following primary 
and secondary treatment, such as was done in Akumal. 

Comparisons with Temperate Latitude Interface Systems 

Nutrient removal of the Mexican constructed wetland systems compares very 
favorably with those of similar systems previously applied in temperate latitudes. The 
85% BOD removal achieved in the Mexican wetlands (Table 3-21) is in the range of 80- 
90% reduction reported for most wetland systems (EPA, 1992). However, temperate 
latitude wetlands are reported to achieve nitrogen reduction of <30% and phosphorus 
reduction of <15% (EPA, 1992), compared with the Akumal data which indicate 
reductions of 79% for nitrogen and 77% for phosphorus (Tables 3-19, 3-17) respectively. 
Reduction of coliform bacteria is generally 90-99% (EPA, 1993b), while the Yucatan 
wetlands have averaged over 99.8% removal over the course of this study (Table 3-27). 

Table 4-1 compares the Akumal wetland units with average values for subsurface 
and surface flow wetlands in North America (Kadlec and Knight, 1996). BOD loading 
for the Akumal wetlands is slightly higher than the average subsurface wetland and 
removal rates are higher (88% vs. 69%). Total phosphorus loading in Akumal is less than 
40% that of average North American systems and removal is 76% vs. 32%. Nitrogen 
loading in Akumal is around 4/5 that of typical subsurface flow wetlands, and removal 
efficiency is 79% vs. 56% for North American systems. 

Many subsurface flow wetlands in temperate climates are started with just a few 
plant species, often virtually monocultural systems. These systems composed exclusively 



255 



Table 4-1 Comparison of loading rates and removal efficiency of Akumal treatment 
wetland units with average North American surface and subsurface flow wetlands 
(Kadlec and Knight, 1996). 

Parameter Wetland system In Out Removal Loading 

mg/1 mg/1 % 



BOD Akumal wetlands 145 17.6 87.9 32.1 

(Biochemical 

oxygen demand) 

Average temperate surface 30.3 8.0 74 7.2 

flow wetlands 

Average temperate subsurface 27.5 8.6 69 29.2 

flow wetlands 

TP Akumal wetlands 8.05 19 76 4 17 

(Total 

phosphorus) 

Average temperate surface 3.78 1.62 57 0.5 

flow wetlands 

Average temperate subsurface 4.41 2.97 32 5.14 

flow wetlands 



TN 


Akumal wetlands 


47.6 


10.0 


79 


10.3 


(Total nitrogen) 














Average temperate surface 


9.03 


4.27 


53 


1.94 




flow wetlands 











Average temperate subsurface 18.9 8.41 56 13.19 

flow wetlands 



Note: Akumal wetland data based on loading of 2.7 m3 wastewater per day 
on area of 130 m2, using average wastewater data from this study. As designed, 
full loading would be over twice as much. 



256 

of Typha latifolia, Scirpus spp. or Phragmites australis are less attractive and less 
beneficial for wildlife. However, some large surface flow systems have included natural 
wetlands and been managed to foster a wider biodiversity of plants and habitats (Kadlec 
and Knight, 1997; Reed et al, 1995). 

Comparison of Emergy Indices of Akumal Units 

Table 4-2 summarizes the emergy evaluation of the treatment system as compared 
with a package plant treatment and a larger conventional treatment system at the 
University of Florida (see Appendix C). Figure 4-1 presents an aggregated systems 
diagram of the Akumal treatment units and mangroves with flows of emdollars. 

For the Akumal treatment wetland units, the majority of emergy apart from 
sewage was from local sources. These inputs include wind energy, limestone gravel, 
limestone rock, and wetland plants. Purchased, imported goods are less than one-third of 
the total emergy (excluding that of the sewage itself) in the systems. Since the 
construction was labor-intensive, requiring local workers for excavation, construction of 
the concrete liners and placement of the gravel, the system to a large extent draws on and 
keeps both monetary transactions and emergy within the area. 

By contrast the University of Florida system derives over 220 times more emergy 
from purchased goods and services than from free environmental resources (excluding 
the wastewater) and the package plant derives over 2600 times as much emergy from 
purchased goods and services rather than from free environmental resources. 

The transformity of the output (treated effluent) (6.85 E6 sej/J) from the wetland 
system is higher than that of the Akumal package plant (4.83 E6 sej/J) reflecting the fact 



257 



Table 4-2 Comparison of emergy indices for Akumal treatment units, package plant at 
Akumal and the University of Florida wastewater treatment system (Appendix C). 



a/ Based on transformity for wastewater calculated as co-product of total emergy required 
to support people 



Emergy index 


Akumal wetland 
units 


Package plant at 
Akumal 


University of 
Florida conventional 
treatment system 



Purchased / Free 0.39 2,693 220 

(excluding sewage) 

Transformity of output 6.85 E6 sej/J 4.83E6sej/J 4.71E6sej/J 

Empower density 2.5 E19 sej/ha/yr 7.4 E19 sej/ha/yr 14.3 E20 sej/ha/yr 
(emergy/area/time) 

Purchased emergy per 0.3 E14 sej 2.3E14sej 1.0E14sej 

person 



b/ Based on transformity of wastewater of 1.0 E6 sej/J (food/services/water used) 



Emergy index 


Akumal wetland 
units 


Package plant at 
Akumal 


University of 

Florida treatment 

system 



Purchased / free 0.39 2,693 220 

(excluding sewage) 

Empower density 6.2 El 8 sej/ha/yr 1.95 E19 sej/ha/yr 3.3 E20 sej/ha/yr 
(emergy/area/time) 



Purchased emergy per 
person 

Emergy jper person 


0.3 E14 sej 

2.4 El 4 sej 


2.3 E14 sej 
2.5 E14 sej 


1.0E14sej 
72.8 E14 sej 











258 



Sewage 




Free environmental 
resources 



From the economy 



[Environment] ^- 




Limestone Wetland 
Treatment System 



Emdollars 
(thousands) 



258.5 

— ► 



Water 



Figure 4-1 Diagram showing annual 
emdollar contributions in the constructed 
wetland system in Akumal, Mexico. 



259 

that far less treated wastewater is discharged from the constructed wetland, since more 
wastewater is utilized within the system. Such use of emergy within the system rather 
than passing it out helps produce a high quality ecosystem. The wetland transformity for 
treated wastewater is also higher than the University of Florida system (4.71 E6 sej/J) 
perhaps reflects the economy of scale of a large wastewater plant and its very large 
throughput of wastewater. 

Though the Mexican wetlands use a far greater proportion of locally available 
resources, and little purchased goods, such systems require more space (land area) per 
person and time (hydraulic residence time) than large conventional treatment systems 
utilize. 

The Akumal wetlands use less than 1 5% the purchased emergy per person 
compared to the package plant (0.3 E14 sej vs. 2.3 E 14 sej) while the University of 
Florida facility uses three times as much purchased emergy per person (1.0 E14 
sej/person). The wetlands have the lowest empower density, with the package plant 
almost three times greater, and the University of Florida system being the highest (Table 
4-2). 

Table 4-2 also presents the results of emergy comparisons if the treated sewage is 
treated as a product of the food, water and services supporting their population, rather 
than as a co-product of the total emergy support. Green (1992) calculated the 
transformity of raw domestic wastewater to be 5.54 E5 sej/J for Nayarit, Mexico. 
Bjorklund et al (1998) calculate a transformity of 5.46 E6 sej/J for Sweden. Using a 
transformity in-between these values (1 E6 sej/J) since Akumal has many of the 
characteristics of a developed economy in its reliance on imported foods. Using this 



260 

transformity for wastewater has the consequence of reducing emergy flows by around 
4.5. However, the main relationships observed between the limestone wetland units, 
package plant at Akumal and the University of Florida system persist. The purchased to 
free environmental ratio is unchanged, and the wetland systems still have the lowest 
empower density and the lowest emergy use per person (Table 4-2). 

Role of Limestone Substrate 

Unlike unreactive gravel (igneous and metamorphic rock) that has been 
predominantly used in subsurface flow wetlands, the use of local limestone as the 
primary substrate in the Mexican wetland units was important in controlling and 
stabilizing its biogeochemistry and treatment efficiency. 

Limestone is predominately calcium/magnesium carbonate and its chemistry is 
dominated by the common ion effect which carbonate dissociation shares with the 
hydration of carbon dioxide (to form carbonic acid). The pH of the water determines 
which form, H 2 C0 3 , HCO3" 1 or C0 3 2 , will predominate in the system. 

In subsurface wetland units, where water level is kept below ground, algae and 
aquatic plants are absent. Photosynthesis occurs above the limestone/wastewater level. 
Thus photosynthesis had little impact on carbon dioxide levels in the underground. 
Instead, respiration by roots and bacteria increased carbon dioxide concentrations in the 
water column. 

Limestone also aided phosphorus removal because of the reaction of calcium with 
phosphate, as was illustrated in the laboratory experiments conducted during this study 
(Table 3-31). This is especially the case in these alkaline conditions, where reactions 



261 

with calcium and magnesium are the main determinants controlling phosphorus fixation 
(Reddy and D'Angelo, 1994). 

The addition of organic materials with the wastewater probably increased 
microbial respiration and C0 2 production. However, increase in carbon dioxide was 
buffered by reacting with the limestone to form bicarbonates. In contrast, anaerobic 
decay reactions, which predominate in a subsurface flow wetland using wastewater high 
in sulfates, tend to increase carbonate saturation and deposition (Drever, 1988). 

Just as the dissolution of limestone is the controlling geochemical reaction in the 
Yucatan region, we can also anticipate the slow dissolution of the large quantity of 
limestone initially placed in the Mexican wetland units. Indeed, observations of 
discharge water from the treatment cells reveals a whitish color, indicative of carbonate 
dissolution materials. 

Seasonal Changes and Effect of the Dry Season 

Although the climate of the Yucatan has a sharp dry season, the coastal 
microclimate is moderated by steady flows of maritime tropical air from the east 
augmented by the sea breezes. Annual temperatures do not show great variability in the 
Yucatan, with the hottest average monthly temperature (26.2 deg. C.) occurring in June, 
and the lowest 23.1 deg. C. in December (Viquiera et al., 1994). Average relative 
humidity is even more constant, with a high of 88% in September and the low in 
March/April with 81% (Ibarra and Davalos, 1991). As a consequence, potential 
evapotranspiration is high year-round, averaging 4-5 mm/day in the rainy season yet still 



262 

3 mm/day in the dry season. (SARH, 1997). Conditions were uniform enough for 
vegetation to flourish through wet and dry seasons. 

The Yucatan is a region with a marked period of higher monthly rainfall, May 
through October when over 70% of the 1 100 mm annual rainfall occurs, and a drier 
season, November through April (Viquiera et al., 1994). 

During the warmer, rainy months, direct rainfall and freshwater subsurface inflow 
from inland result in larger groundwater prominence of the freshwater, and in a net 
freshwater discharge to the sea. Consequently, there is a seasonal variation in salinity in 
the water supply of the treatment units and in the mangroves which receive their 
discharge effluent. 

Average phosphorus and nitrogen reductions were slightly greater in the dry, 
cooler months with 79% and 81% reductions compared to 74% and 68% reductions, 
respectively, in the warmer, rainy season. But biochemical oxygen demand reduction was 
greater in the warmer, rainy months with 94% reduction vs. 86% in the dry cool season. 
(Tables 3-17. 3-19 and 3-21). 

The two-year data suggest that constructed wetlands for sewage treatment in the 
Yucatan can remain quite effective in its treatment results year-round. Even in the drier 
winter months, solar insolation and warm temperatures permit active growth of 
vegetation and high metabolic functioning of microbes, since adequate water and 
nutrients are maintained though sewage inputs to the system. Hydraulic residence is 
longer, since rain dilution of the wetlands is less. Treatment efficiency in the wet season 
is assisted by higher average air temperatures, but diminished by loss of insolation 
through cloud cover and dilution by rainwater. 



263 
Treatment of Wastewater Containing Sea Salt 

The wastewaters at Akumal are salty because the town water supply is pumped 
from groundwater where there is mixing of seawater with freshwater. The high biological 
diversity maintained by the Akumal systems showed that the regional vegetation was 
adapted to salinity in this range. These biodiversity results were in contrast to the lower 
diversity saltwater wastewater mesocosms studied in North Carolina (Odum, 1985). 

The salt content of the wastewater may be a contributing factor in the 
establishment and maintenance of high plant biodiversity. Species tolerant of high salt 
content, such as occur nearby in the mangrove wetlands, have been able to survive in the 
system, as have many non-halophytic plants that are able to withstand the moderate 
salinity of the wastewater and salt aerosols carried from the sea. Indeed, having an 
intermediate salinity may have been a factor holding in check species capable of 
aggressive dominance (e.g. Typha spp.). 

The wastewater being treated in Akumal is saline, generally averaging 3-5 ppt 
salt. This is in marked contrast to most wastewater treatment facilities that handle fresh, 
originally potable water. The presence of seawater means that in addition to NaCl, there 
is a strong presence of sulfates, since seawater contains 2700 mg S0 4 /1 on average (Day 
et al, 1989). In the anaerobic conditions of wetlands containing saltwater, sulfate 
reduction usually dominates rather than the methanogenesis that often prevails in 
freshwater conditions. This is attributed to the competition for electron donors, the larger 
thermodynamic yield and higher affinity of sulfate reducers to utilize compounds 






264 

potentially usable by methanogenic bacteria (Capone and Kiene, 1988; Achtnich et al, 
1995). 

Simulation of Hydrological Extremes 

Simulations of the water budget model for the wetland treatment unit and 
mangroves indicate water flows and turnover times that help understand the processing 
of the various inputs. "What if?" experiments with the model suggest the range of water 
volumes that may develop with extreme events. Simulations were conducted examining 
the impacts of hurricane events, increased population and sewage loading, and decrease 
of inland groundwater due to interior development. 

Increasing population so that wastewater inputs are ten times greater results in 
increased water levels in the mangrove, and increases biomass especially in the treatment 
wetlands (Figure 3-57). Development inland reducing groundwater discharge to the 
mangroves, has the effect of lowering groundwater levels in the mangrove, results in 
diminished water level (Figure 3-58). A hurricane producing heavy rainfall, high tides 
and winds that reduce vegetation by half in the wetlands and mangroves leads to 
increased flow of treated effluent into and out of the mangroves. Recovery of vegetative 
biomass to previous levels requires years. The high tides are quickly flushed, so that the 
flooding of the mangroves is a transient event (Figure 3-59). 

Transpiration of Treatment Systems 

Because vegetation productivity has been related to transpiration, an estimate of 
transpiration of the Akumal treatment systems is a productivity index as well as a major 
component of the hydrological budget. Evaporative water loss was limited since 



265 

wastewater was maintained below the surface of the wetland, air exchange was reduced 
by the dense plant canopy (Table 3-14 and Table 3-15) and because the ground was 
mulched and shaded. 

Loss of water through transpiration increases total treatment efficiency of 
the Akumal wetland compared with conventional sewage treatment facilities. The 
residence time in conventional treatment sewage facilities is 2-4 hours, allowing for little 
loss from evaporation, so that virtually all the influent water leaves the system. However, 
in the wetlands, the loss of 20-30% of water through transpiration means that total 
pollutant removal on a mass balance basis is greater than is indicated by discharge water 
analysis alone. For example, if P levels in the discharge water are 75% lower than those 
in the septic tank in the wetlands, and transpiration removes 20% of the wastewater, 
actual phosphorus reduction totals 80%. If transpiration is 30% of wastewater, then 
phosphorus removal increases to 82.5%. 

Transpiration of freshwater tends to increase salinity of the wastewater in the 
treatment units, since relatively freshwater is lost through plant leaves. However, the 
measured salinity in the treatment cells over the course of this study showed 
predominantly a slight decrease in salinity (Table 3-26), presumably because of dilution 
by rainfall on the wetlands. 

Maintaining Vegetative Biodiversity 

In the two-year study, survival of planted species and environmental seeding 
produced a dense, high diversity ecosystem. Maintenance of high biodiversity long-term 
will require successful re-establishment of seedlings of the wetland plants. Some of the 



266 

loss of species already seen may have resulted from the death of annuals, and the 
suppression of lower canopy plants and seedlings due to shading (Table 3-1). 

The maintenance of high species diversity is of theoretical interest. Some of the 
factors which may have helped maintain diversity and prevented a few species from 
dominating the system are 

1. the use of slightly saline which allows a range of both freshwater and salt-tolerant 
plants (as noted above). 

2. continued inputs of nutrients which may act as a stress keeping the ecosystem in a 
productive, intermediate stage between primary succession and maturity (Odum, 1994). 

3. nearly constant water temperature (27 ± 0.5 °C year-round) 

4. the pulses of nutrient input which low and high tourist season occupancy produce. 

Impacts of Effluent Disposal on the Mangroves 

Results from the present study have shown that there has been an only moderate 
increases in nutrient levels in mangrove groundwater (Table 3-46, Table 3-47) and soil 
sediments (Table 3-43, Table 3-45). Longer-term effects on the mangroves need to be 
assessed. 

Feller (1995), Lugo et al (1976), and Sell (1975) indicated that mangroves 
typically are nutrient limited, both for nitrogen and phosphorus and can increase 
productivity with added nutrient inputs. Walsh (1967 cited in W.E, Odum et al, 1982) 
found mangroves were net sinks for nitrogen and phosphorus. Nutrients are removed in 
mangrove ecosystems by prop root periphyton, the fine root system, organic sediments, 












267 

algae and bacteria/fungi. Thus, there is a good likelihood that mangroves will continue to 
be effective at nutrient removal from wastewater discharge. 

Clough et al (1983) expressed concerns that the addition of water containing 
organic carbon compounds will lead to increased anaerobic conditions in the sediments, 
further lowering redox potentials. However, WE. Odum et al. (1982) note that the 
sediments underlying many mangroves tend to be very anaerobic, with redox values of - 
100 to -400 mv, due to their high organic matter content. The 75-80% organic matter 
content in the Akumal mangroves before wastewater discharge exceeds the 10-20% 
considered more typical of mangrove soils and is indicative of isolation from tidal 
erosion (W.E. Odum et al, 1982). 

After discharge of treated sewage, salinity levels were reduced (Table 3-52), and 
the small extent of phosphorus increase in soil sediments indicate phosphorus use by the 
mangroves (Table 3-45). 

Carrying Capacity for People - Coastal Development Potential 

To anticipate the potential value of these wetland treatment units in preventing 
pollution caused by tourist development, an emergy evaluation was made of a developed 
square kilometer of coastline around the Akumal study site, supporting 225 people and 
employing 125 people (Table 3-55). 

Without a good treatment / recycle system large amounts of anthropogenic 
organics, nutrients, and coliform bacteria will be released into the coastal and marine 
environment (Table 3-58) with impact on coral reefs, beaches, health and tourist 
economy. In addition, if development results in further loss of the mangrove areas, 



268 

nutrients flowing subsurface from inland sources that are currently intercepted will also 
be discharged to the marine environment. Thus, future planning should ensure adequate 
area is left in all developments for installation of adequate wetland treatment areas to 
absorb the additional nutrient loading tourist development brings. Needed for one 
kilometer of coastal development supporting around 250 people are some 900 square 
meters of constructed wetland, plus 1-2000 square meters of mangroves. 

Currently development is concentrated on the coastal zone itself, but the location 
of more human population and/or industry in inland areas will impact sustainability of 
coastal resources by diverting groundwater and increasing nutrient loading of remaining 
groundwater. 

Percent of Economy Required for Wastewater Processing 

Kadlec and Knight (1996) indicated that constructed wetlands are at least 50% 
less expensive than conventional sewage treatment in capital costs. Operational and 
maintenance costs are even lower, averaging 10%. However, this varies considerably, 
depending on land costs. 

Tables 3-34 and 3-35 show the economic advantages of the Akumal wetland 
treatment. Capital costs for the limestone wetlands were around $165/person compared 
to $385/person for a package treatment plant; and maintenance costs for the wetland 
were $3/person compared to $27/person for the package plant. On a regional basis, the 
constructed wetlands would require 0.3% of yearly monetary flows along a square 
kilometer of developed coastline, vs. 1.1% for the package plant (Table 3-34, Table 3-35 
and Table 3-55). 



269 



The limestone wetlands cost approximately $450 per year (over its 20 year 
anticipated operation) to treat 3000 gallons per day, which is $0. 15 per gallon of 
wastewater. This is considerably lower than the $0.62 per gallon reported in a survey of 
subsurface flow wetlands in the United States (EPA, 1993b). This may reflect lower 
labor and construction costs in Mexico, as well as the fact that the research wetlands 
entailed no land costs, as they were built on land already allocated for landscaping 
purposes. 

Perspectives from Regional Simulation Model 

A regional simulation model was developed in order to elucidate a few of the 
important interactions between the natural environment and the human economy 
including tourism in the Yucatan. Figure 4-2 shows the systems diagram with equations, 
Figure 4-3 shows calibration storages and flows and Figure 4-4 shows a simulation run of 
the model showing changing levels of assets, coral, algae, nitrogen and image as 
development proceeds. Table 4-3 presents the program in BASIC for the simulation 
model. 

In the systems diagram, algae (A) and Coral (C) compete for sunlight energy (J), 
with some sunlight (Rj) going to the algae and a portion of the remainder (R 2 ) to the 
corals. Algal growth (k0 is autocatalytic, using sunlight, nutrients (N), and algal standing 
biomass for increase, and declining through respiration/death (k 5 ). Coral growth is also 
autocatalytic, depending on the interaction of sunlight and coral biomass. Natural coral 
losses (k 13 ) are augmented by anthropogenic damage linked to increased development 
(k 16 ). Coral presence adds to the regions image (I), which in turn helps attract income 




Rl = J/(l + k!*N*A) "^- dJ = k 7 *C - k 14 *l 

R2 = Rl/(1 + k 2 *C) dS = k 9 *S*M/P 1 - k 13 *S 

dA = k 4 *R!*N*A - k 5 *A dM = k n *l*Td - k 12 *M 

dC = k 3 *R 2 *C - k 6 *C*S - lc! 6 *C 

dN = Jn + k 10 *S*(M/Pl) - k 8 *N*R!*A - k 15 *N 



Figure 4-2. Systems diagram and difference equations used for simulation model of the 
!£*££" thS natUrnl enVif0nment and the human econom y al °ng the Yucatan 



271 



no 

\ .25 t fl mage 
0.5 

N 0-25\V Ifrouristel 







Figure 4-3. Systems diagram for Yucatan coastal model. Values shown are steady-state 
storages and flows between components. 









272 



Assets (S) 160 
Nitrogen (N) 320 
Coral (C) .160 
Algae (A) 160 
Image (I) 6.4 




Time 



Figure 4-4 Computer simulation of the Yucatan coastal model. The legend gives the full 
scale values of the ordinate for each quantity. 



273 



Table 4.3 Program in BASIC for simulation model of interactions between natural 
environment and human economy along the Yucatan coast. 



10CLS 

20 Screen 0,1 

30 Color 0,1 

40 Line (0,0X320,180), 1,B 

60A = 5 

70 C = 95 

80 N = 10 

901=1 

110 S= 10 

120M-1 

150Td = 50 

160 J= 100 

165 No = 5 

170 Rem Coefficient values 

172 PI = 100 

175 T=l 

1 78 dt = 0. 1 

1 80 kl =0.0000958 

190 k2 = 0.020606 

200 k3 = 1.212121 E-3 

210 k4 = 7.492537 E-4 

220 k5 = 0.5 

230 k6 = 0.0001 

240 k7 = 0.002 

250 k8= 1.492537 E-4 

260 k9 = 0.5 

270kl0 = 9.5 

280 kl 1=0.4 

290 kl2 = 1 

300 kl3 = 0.05 

310kl4 = 0.2 

320kl5 0.5 

330 kl6 = 0.03 

Rem Scaling factors 

350 A0 = 2 

360 TO = 1 

370 CO = 2 

380 NO = 1 

390 SO = 2 

400 M0 = 2 

41010 = 50 



440PSET(T, 180-I/I0), 3 

420PSET(T, 180-A/AO), 1 

430PSET(T, 180-C/C0),2 

440PSET(T, 180-I/I0), 3 

480PSET(T, 180- S/ SO), 4 

490PSET(T, 180-M/M0),5 

500PSET(T, 180-N/N0),6 

505 PSET(T, 180-A/AO), 1 

510PSET(T, 180-C/C0),2 

540Rl=J/(l+kl*N*A) 

550R2 = Rl/(l + k2*C) 

560 dA = (k4*Rl*N*A) - (K5*A) 

570 dC = (k3*R2*C) - (K6*C*S) - (K16*C) 

580 dS = (k9*S*M / PI) - (K13*S) 

590 dM = (kl l*I*Td) - (K12*M) 

600 dN = No + (K10*S*(M/P1)) - (K8*N*R1*A) 

-(K15*N) 
610dI = (K7*C)-(K14*I) 
620 A = A + dA*dt 
640 N = N + dN*dt 
660 T = T + dt 
700 IfN<0 then N = 
710 IfA> 100 then A =100 
720 IfC > 100 then C= 100 
730IfA<0thenA = 
740IfC<0thenC = 
750IfM<0thenM = 
760 IfT< 640 goto 540 
770 Print "A=", A; "C=", C, "N=", N. "S=", S 



274 



(k n ) from tourism (Td). This income adds to the region's money (M) and is used (k 12 ) to 
purchase goods and services (Gs). The growth of development structure (S) is 
autocatalytic (k ]5 ) from the interaction of goods and services (Mk^/Pi) and existing 
structure. The increased development process both increases coral loss and adds (k 10 ) to 
the quantity of nutrients (N) which can impact the natural environment. Nutrients receive 
a flow from the natural environment (J n ) as well as from economic development (k 10 ), 
while some of the nutrient outflow is taken by algae (k 8 ) and the rest goes to the deeper 
ocean (ki 7 ). 

The coral reef plays a major role in sustaining the positive image of the region, 
which helps attract investment and tourist flow to the region. Decreased coral cover 
resulting from development without adequate sewage treatment increases algal 
domination, which acts to lower the image, thus dampening tourist development. Over 
time, these balance, and the overall system adjusts to a level of development far below 
the early "boom". Coral cover at first rapidly decreases, then recovers as development 
tapers down (Figure 4-4). 

Simulation results are sensitive to starting conditions. If nitrogen begins at much 
higher levels, tourist development peaks at far lower levels, and the system regains a 
steady state earlier (Figure 4-5a). If coral begins at zero, the system crashes since there is 
no pull for continued investment and tourist development (Figure 4-5b). If assets and 
money begin at much lower levels, the process of boom takes longer to develop, but rises 
to a greater peak, and steady state conditions at the end have less coral cover than under 
the model's standard run (Figure 4-5c). 






275 



a/ 





A v \ v 


Assets (S) 160 

Nitrogen (N) 320 
Coral (C) .160 
Algae (A) 160 
Image (I) 6.4 


a. 


fj 









b/ 



1 

1 

i 


Assets (S) 160 


i 


Nitrogen (N) 320 




Coral (C) .160 




Algae (A) 160 


I 


Image (I) 6.4 


fh M 




r ^S. ■ 





c/ 









Assets (S) 


160 








Nitrogen (N) 320 








Coral (C) 


160 








Algae (A) 


160 


c y^ 


>\ \ \ 


IV 


Image (I) 
i 


6.4 


I^J 





















Figure 4-5 Simulation runs of the interaction of the environment and human economy in 
the Yucatan, a/ Impact of starting with nitrogen at ten times higher value b/ Impact of 
starting with coral at zero c/ Impact of starting with money and assets at 1/10 value. 



276 

The model simulates some components of the present situation in the Yucatan, 
since diving, snorkeling and fishing are a significant part of the tourist appeal of the area. 
Most of the hotels offering coral reef exploration now have inadequate sewage treatment, 
and much current development is threatening other parts of the environment, such as 
mangroves, which help protect the marine environment. If the coral reef suffers great 
degradation (as occurred in Jamaica), it seems clear that tourist revenues will decline as a 
result. 

Future Potentials of the Designed Treatment System 

The scope for application of the wetland treatment system along the Yucatan 
coast is great. Already, interest in such systems from those who have seen the prototype 
systems at Akumal has led to some fifteen additional systems being built from Tulum to 
Playa del Carmen.. The scale thus far has been from individual house systems, 
hotels/condominiums of up to 50 people, and a theme park with 1500 visitors per day. In 
the Cancun area, the government has decided that no new connections will be made to 
the existing municipal sewage treatment plant, which is already over-loaded, obliging 
new businesses and homeowners to do on-site treatment. The principal advantages that 
have attracted new applications are the low-cost and low-maintenance of the wetlands, 
plus their attractiveness. 

To lower costs of larger systems, it is anticipated that rubber or polyethylene 
liners will be used instead of concrete. Each new system has served as a testing ground 
for planting new plant species, and an additional 10-15 palm, tree and shrub varieties 
show promise of doing well in the wetland systems. The search for suitable wetland 



277 

plants that have economic potential continues. Already, bananas in several systems have 
successfully produced fruit. Several of the palms in the Akumal systems have value as 
thatching material. In order to develop systems which will be inexpensive enough to be 
used by local Mayan families and communities, construction costs need to be lowered 
and more useful products produced. Ideally, it may be possible for a local family or 
community to build such systems themselves (thus lowering construction costs) and to, 
contract with local farmers to maintain the system in return for harvesting rights. 

Long-Term System Prospects 

It is unknown how long the wetland system will remain effective at sewage 
treatment. A number of subsurface flow wetlands have been operating successfully for 
over 10-20 years (Kadlec and Knight, 1996; EPA, 1992). While BOD reduction tends to 
be adequate, phosphorus and nitrogen removal have sometimes been inadequate in 
wetlands constructed in temperate latitudes (EPA, 1992). 

The limestone may remain effective at phosphorus uptake for a considerable 
time, as its starting concentration was quite low (40 mg/kg). The 6 mg P/kg uptake of the 
limestone during the first year of operation may reflect the rapid increase in plant and 
microbial biomass during early succession in the wetlands. It is to be expected that biotic 
primary productivity will decline or stabilize as time goes on, thus placing increasing 
importance on the limestone to act as a sink for influent phosphorus. 

The phosphate mining district of Florida demonstrates that phosphate 
substitution for carbonate in limestone (over geologic periods) can continue indefinitely, 
producing minerals that are 5-20% phosphorus (Gilliland, 1973: Odum et al, 1998). At 



278 

the rate of 50-100 mg/kg of phosphorus enrichment, it would take some 100-200 years 
before the wetland limestone gravel reaches 1% phosphorus content. While occupation of 
surface area may be a limiting factor in such uptake, bioturbation and the high 
porosity/permeability of limestone may continue to ensure continued uptake. 

Nitrogen removal by the wetlands increased over the first two years of operation, 
as plant productivity and root penetration of the subsurface zone increased. From half to 
two-thirds of nitrogen removal in constructed wetlands comes from gaseous release of 
the nitrogen after nitrification/denitrification processes (EPA, 1992). Therefore, 
oxygenation of the rhizosphere by plant roots is an important factor, for otherwise only a 
reducing environment might prevail under the surface of the limestone. The inclusion of 
wetland species able to deeply penetrate, and the inclusion of a diversity of plant species 
with varying rooting patterns, may help to maintain adequate oxygenation 

For the Akumal system, the inclusion of the mangrove as a final treatment step 
gives a safety factor for ensuring continued effective wastewater treatment. Should 
additional nutrients be discharged from the constructed wetlands, the mangroves may 
help prevent additional nutrients from reaching marine ecosystems. This may be 
especially true for phosphorus which is the most limiting nutrient for mangroves along 
this coastal zone (Feller, 1995). 

The diversity of the wetland vegetation may also offer long-term performance 
benefits, as it will tend to make the system less prone to system failure due to disease or 
other plant failure than if the system was dominated by several plant species. 



279 

Hurricane events, which are a periodic event along the Yucatan coastline, may act 
to "reset the successional clock", dramatically decreasing canopy cover and system 
biomass in both constructed wetlands and mangrove ecosystems. 

In the event of long-term decrease of limestone uptake of P below acceptable 
levels, or to decrease of system performance because of clogging through deposition of 
sewage solids or organic material, the system may be regenerated by installation of fresh 
limestone. The old limestone may be used as a slow-release fertilizer for area gardens or 
farms. Since the limestone accounts for less than 20% of original construction costs, it 
will be cost-effective to replace the limestone on this periodic basis if necessary. 

Authorization Meeting in Mexico 

On August 18, 1998, representatives of Planetary Coral Reef Foundation, Mexico 
were invited to the University of Quintana Roo at the state capital of Chetumal in order 
to present the limestone wetland systems to the faculty and federal and state government 
agencies. Those present included the Commission National de Agua (CNA) and Recursos 
Naturales y Pesco de Quintana Roo. 

Results from the present research study were presented, as well as many of the 
additional systems that have been built along the Yucatan coast to date. Questions raised 
following the presentation covered the economics of wetland treatment compared to 
other alternatives, the impact of catastrophic events such as hurricanes, the mechanisms 
responsible for nutrient uptake and coliform reduction, and the methods by which larger 
cities might benefit from such approaches. 



280 

Many of those present indicated that there is growing concern in the government 
and university that the development in the northern portion of the state, and particularly 
Cancun, was allowed to proceed too rapidly. Thus, there was inadequate regard for issues 
such as preservation of key ecosystems, such as the mangrove and other wetlands, and 
before adequate sewage treatment systems were available. The southern portion of the 
state (from the Sian K'an Biosphere Reserve to the Belize border), is still in very early 
stages of tourist and other development, and could still put in place better measures for 
integration of the human and natural environment. 

At the conclusion of the three hour meeting, the head of the University of 
Quintana Roo, Rector Efrain Villaneuva Arco, announced support of the installation of a 
demonstration limestone wetland to treat the sewage of 200 people at the University as a 
facility for on-going research and education. The author was invited to design the 
wetland, working with faculty of the University who are developing improved designs for 
septic tanks which will serve as the primary treatment of the system. 

Questions for Research 

Important topics that need future research are the following: 
Biodiversity 

What impact does the presence of high biodiversity have on system performance 
in treating wastewater? Will anaerobic conditions in the subsurface rhizosphere limit the 
variety of plants? Can such high biodiversity be maintained long-term? Which factors are 
responsible for the maintenance of high biodiversity (salt, nutrient inputs, original 



281 

planting, proximity to seed sources, wind or animal seed dispersal)? With increasing 
scale of such wetland systems, will biodiversity patterns be different? 
Mangrove Change 

Will the mangrove ecosystem be fundamentally altered by the addition of treated 
effluent? What impact will be seen on growth rates of different mangrove species, and on 
other system parameters such as canopy closure, soil depth, hydrological regime, species 
abundances? What impact will wastewater effluents have on permanent and migratory 
fauna that utilize the mangroves? What loading ratios will sustain mangroves? 
Useful Life of the Wetland System 

What is the likely longevity of the wetland treatment units? Will there be gradual loss of 
hydraulic conductivity, and at what rates, through deposition of secondary minerals, 
suspended solids or filling of void spaces by deposition of peat from anaerobic carbon 
reduction? Will the limestone continue to play a role in the retention of phosphorus, or 
will this be diminished over time as gravel surface area is occupied? Will bioturbation 
ensure continuous availability of limestone substrate for phosphorus reactions? 
Acceptability and Affordability by Local People 

What modifications, such as using geomembrane liners rather than concrete, can be made 
to further lower construction costs? Can the systems be made profit creating rather than 
simply low-cost by concentrating on the inclusion of usable products (timber, fuel, food, 
and fiber) which can be harvested from the wetland units? Which products are most 
desired by and acceptable to the Mayans living in the area? 



282 
Summary 

Over the course of a two year study, a new system of limestone subsurface flow 
wetlands was developed and coupled to final treatment in mangrove wetlands. The units 
recycled nutrients and improved the quality of saline domestic wastewater. The system 
has maintained a high level of biodiversity of wetland plant species. After two years, the 
upper canopy of wetland palms and trees is 4-5m (13-16 feet) tall with dense canopy 
closure. Canopy closure and Interception of light after just two years is already similar to 
that of natural Yucatan wetlands. 

This system is inexpensive and with advantages over alternative sewage treatment 
approaches in using a preponderance of local resources, few imports, and little use of 
machinery and electricity. Its two stages were adapted to the hydrogeological setting of 
the Yucatan coast; limestone gravel helped ensure adequate treatment before release, and 
natural mangrove wetlands were utilized as the most appropriate biofilter for nutrients 
remaining in the effluent from the constructed wetlands. 

Emergy evaluations show the ratio of imported inputs to free, environmental 
inputs is small. Economically, the system compares favorably in having low capital and 
operating costs. In addition, there are aesthetic benefits, habitat protection for wildlife, 
and producing useful products such as fruit, fiber, building materials, etc. 

Yucatan limestone used in the system contains very little phosphorus, and the rate 
of increase during operation was small, suggesting the substrate may remain effective in 
phosphorus uptake long-term. Nitrogen and phosphorus increase in the mangrove soils 



283 

was small (<15%). Coliform bacteria concentrations and chemical oxygen demand were 
at background levels within 6 m of discharge. 

The eastern Yucatan is in the midst of extremely rapid tourist development. The 
present work demonstrates the feasibility of designing and implementing ecological 
engineering solutions that can help integrate the human economy with the natural 
environment. This wastewater treatment system has potential for more widespread 
application in tropical coastlines and countries that are in great need of low-cost, low- 
tech solutions that employ natural systems to solve environmental challenges. 



APPENDIX A 
CHART RECORDER DATA FOR AKUMAL 












284 




Figure A-l Water level record for cenote near wetland treatment unit, 27-28 May 1997. 







F Ig ureA-2 Water level record for 



cenote near wetland treatment unit, 28-29 May 1997. 



MiH-T^r^^ 




Figure A-3 Water level record for cenote near wetland treatment unit, 29-30 May 1997. 




Figure A-4 Water level record for cenote near wetland treatment unit, 30-3 1 May 1997. 



289 




Figure A-5 Water level record of tidal heights at Yal-Ku Lagoon, 27-28 May 1997. 



290 



Vizi" 




Figure A-6 Water level record of tidal heights at Yal-Ku Lagoon, 13-16 December 1997. 



291 




Figure A-7 Water level record of tidal heights at Yal-Ku 



Lagoon, 16-17 December 1997. 


















292 




Figure A-8 Water level record of tidal heights at Yal-Ku Lagoon, 17-19 December 1997. 



293 




ia/Zo 



ia/il 



Figure A-9 Water level record of tidal heights at Yal-Ku Lagoon, 19-22 December 1997. 



^fess 



^5S E^E£^^ 




Figure A-10 Water level record for cenote near wetland treatment unit, 10-14 December 1997. 




Figure A-l 1 Water level record for cenote near wetland treatment unit, 14-17 December 1997. 



** *^ - v t - - - ■ / r s ^ T > 




296 



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Figure A- 12 Water level record for cenote near wetland treatment unit, 17-20 December 1997 



— ,' 



=j^^^^^ ^wyj^ s 



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kes^ffife 



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Figure A- 13 Water level record for mangrove near wetland treatment unit, 9-14 December 
1997. 







Figure A-14 Water level record for mangrove near wetland 



1997. 



treatment unit, 14-17 December 




Figure A-15 Water level record for mangrove near wetland 



treatment unit, 17-20 December 




Figure A- 16 Water level record for mangrove near wetland treatment unit, 18-21 July 1997. 




Figure A- 17 Water level record for mangrove near wetland treatment unit, 22-25 July 1997. 




Figure A- 18 Water level record for mangrove near wetland treatment unit,.25-28 July 1997 



303 







Figure A-19 Water level record of tidal heights at Yal-Ku Lagoon, 24 July - 1 August 1997. 



APPENDIX B 
NOTES AND TABLES FOR WATER BUDGET SIMULATION MODEL 

Notes on literature values used to estimate storage values and pathway flows in 
the water budget simulation model.. 

1. Tides. Tidal range is typically 15-20 cm during full moons with a high of 40 cm and a 
low of 6 cm observed in the last two years (Shaw, pers. comm.) For Puerto Moreles, 
80 km further north up the coast, average tidal height is 18. 1 cm (Ibarra and Davalos, 
1991). 

2. Rainfall. Average monthly rainfall at Tulum, a coastal town 20 km further south of 
Akumal (Viquiera et al, 1994) is presented in Table B-l. Average rain per day is 3.02 
mm. 

3. Potential evapotranspiration (PET). Potential evapotranspiration (PET) measured at 
Tulum between 1983-1996 (SARH, 1997) totals 1450 mm and is shown in Table B-2. 
Average yearly evapotranspiration has been estimated to total 900 mm. Average daily 
PET is 3.99 mm and average daily evapotranspiration = 900/365 = 2.47 mm. 

4. Relative humidity/temperature/saturated and air vapor pressure. Table B-3 shows 
relative humidity, temperature data for the Yucatan coast. Average monthly relative 
humidity for the area according to governmental meteorological data from 1958-1980 
(cited in Ibarra and Davalos, 1991) shows little variance with March at 81% the 
lowest and September at 88% being highest. Temperature is from Viquiera et al, 1994 



304 



305 



for Tulum. Saturated vapor pressure is from temperature tables contained in Lee, 
1978 and air vapor pressure is calculated from relative humidity and temperature 
monthly averages. 

5. Wind. Average wind velocity for the area is 5 m/sec. Table B-4 presents average 
monthly wind velocity (Ibarra and Davalos, 1991). 

6. Inland freshwater groundwater flow. Average groundwater flow was calculated 
(Back, 1985) by dividing drainage area of 65,500 km 2 by coastal length of 1,100 km. 
Of the 8.6 E3 m 3 /yr through each meter of the receiving wetland, Table B-5 presents 
estimates of monthly flow by correlation with monthly share of annual rainfall (see 
note 2). Average daily groundwater flow - 8630/365 = 23.64 m 3 and average monthly 
groundwater flow is 8630 /12 = 719.16 m 3 . In the simulation model, average monthly 
groundwater flow is taken as 0.30 above datum (1 meter below surface of mangrove, 
0.32 m below mean sealevel). The low months (February-April) were taken as 0.2 m 
height of water in mangrove, and top month (May) as 0.6. Therefore, following gives 
monthly values, expressed in height (m) of water in mangrove m2: January 0.254, 
February 0.2, March 0.2, April 0.2, May 0.6, June 0.47, July 0.29, August 0.33, 
September 0.47, October 0.44, November 0.22 and December 0.21. 

7. Solar insolation. The value for solar insolation used by Odum et al (1986) for the 
Amazon is 140 Kcal/cm 2 /yr or 3835 Kcal/m 2 /day, with presumably higher cloud 
interference with solar radiation. Brown et al (1992) use 180 Kcal/cm2/yr forNayarit 
(World Energy Data Sheet), or 4932 Kcal/m 2 /yr. From Sellers' (1965) diagram 



306 



relating latitude to average yearly solar radiation at 20 deg. N latitude gives 1 10 kilo- 
langley/cm 2 /yr =110 Kcal/cm 2 /yr = 3013 Kcal/m 2 /day 

8. Mangrove primary productivity and biomass. Productivity in mangrove swamps 
varies greatly and several characteristic ecosystem types have been traditionally 
identified. Riverine mangroves are the most productive, followed by fringing 
mangrove areas and basin mangroves (Table B-6). Less productive are hummock 
mangroves growing in unfavorable locations. Lugo and Brinson (1979), reviewed the 
literature and gave data on net primary productivity (NPP) of these mangrove types in 
Florida. Using an average value of 1.5% N for mangrove plant tissue, we have 
translated their numbers into average annual N assimilation by mangroves, which 
shows that Nedwell et al's productivity calculation places their mangrove system as 
intermediate between riverine and fringing in N-uptake. Cintron et al (1985) (cited in 
Mitsch and Gosselinke, 1993) give a range of biomass of 0.8 - 15.9 kg/m 2 for fringe 
mangroves and 1.6 - 28.7 kg/m 2 for basin mangroves. We can use an average figure 
of 16 kg/m 2 for this model. 

9. Primary productivity and biomass of treatment wetland unit. Richardson ( 1 979) 
estimates net primary productivity in freshwater marshes as follows: Typha wetlands: 
2740 ± 670 grams of organic matter (m 2H yr" 2 ; reed wetlands {Phragmites communis, 
Scirpus spp., Juncus effwus, Cyperus papyrus) 2100 ± 580 grams of organic matter 
(m2)-l yr-2 and freshwater tidal marshes (Peltandra virginica, Acorus calamus, 
Zizania aquatica): 1600 ± 200 grams of organic matter (m 2 )" 1 yr" 2 . These three data 
average 2154 grams of organic matter (m 2 )" 1 yr" 2 , or 5.9 g (m 2 )" 1 day" 2 . Total biomass 



307 



estimates for tidal marshes range from 0. 145 - 0.725 kg/m 2 for a freshwater tidal 
marsh (Simpson et al, 1983, cited in Mitsch and Gosselink, 1994), to estimates for 
peak standing crop of the salt marsh species Spartina alterniflora of 0.754 -0.903 
kg/m 2 (Hopkinson et al, 1980 and Kaswadji et al, 1990 cited in Mitsch and Gosselink, 
1994), which probably comprise 20-30% of total biomass, and 6.55 kg/m 2 for total 
above and belowground biomass in a Louisiana salt marsh (Buresh et al., 1980 cited 
in Day et al, 1989). We can use 6 kg/m 2 as an estimate for the treatment wetland 
unit's biomass since they include larger tree and palm species as well as wetland 
grasses and shrubs. 
10. Wastewater inputs. At design loading, for the 81.6 m 2 wetland, inputs are 24 people x 
0.1 15 cu m/day = 2.76 m 3 /day / 81.2 m 2 , or 0.034 m/day. Our model will use 0.34 
m/day wastewater input for October - April, and in the off-tourist months of May - 
September, a loading of 0.22 m/day. 



308 



Table B-l Average monthly rainfall at Tulum, 20 km south of study site 



Month 


Rainfall, mm. 


January 


77.9 


February 


41.3 


March 


42.3 


April 


41.2 


May 


166.6 


June 


143.3 


July 


88.1 


August 


101.1 


September 


149.7 


October 


140.9 



November 74.7 
December 57.0 

Total: 1,104.1 

(Viquieraetal, 1994). 












309 



Table B-2 Measured evaporation at Tulum, 20 km south of study site along the Yucatan 
coast. Actual evapotranspiration is estimated at 900 mm for the Yucatan. The last column 
is a calculation of evapotranspiration based on the percentage of yearly evaporation that 
occurs in each month.. 

Month Average monthly potential Percentage of Monthly 

evapotranspiration, mm. Yearly ET, evapotranspiration 

% if year total is 900 mm 



January 


89.2 


6.1 


54;9 




February 


102.5 


7.0 


63.0 




March 


129.9 


8.9 


80.1 




April 


148.1 


10.2 


91.8 




May 


142.1 


9.8 


88.2 




June 


141.9 


9.8 


88.2 




July 


150.8 


10.4 


93.6 




August 


144.1 


9.9 


89.1 




September 


125.9 


8.7 


78.3 




October 


101.8 


7.0 


63.0 




November 


94.5 


6.5 


58.5 




December 


83.8 


5.7 


51.3 






1454.6 (Total) 


100 


900.0 




(SARH, 1997). 

















310 



Table B-3 Average monthly relative humidity, temperature and air vapor pressure 
calculated for the given temperature and relative humidity for the Yucatan coast. 



Month 


Average 
relative 
humidity, 
percent 


Temperature 
degrees C. 


Saturated vapor 
pressure at monthly 
average temp., mb 


Air vapor 

pressure 

at average 

relative 

humidity and 

temp. 

for month, mb 


January 


84 


23.3 


28.61 


24.03 


February 


83 


23.5 


28.96 


24.04 


March 


81 


24.7 


31.12 


25.21 


April 


81 


25.5 


32.64 


26.44 


May 


82 


25.8 


33.22 


27.24 


June 


85 


26.2 


34.02 


28.92 


July 


86 


26.0 


33.61 


28.90 


August 


86 


26.0 


33.61 


28.90 


September 


88 


25.0 


31.67 


27.87 


October 


87 


24.9 


31.49 


27.39 


November 


84 


24.8 


31.31 


26.30 


December 


85 


23.1 


28.26 


24.02 


Average 


84 


24.9 


31.49 


26.45 



(Ibarra and Davalos, 1991, Viquiera et al, 1994, Less, 1978) 



311 






Table B-4. Average wind velocity, measured at Puerto Moreles, Mexico, 80 km north of 
study site. 



Month 


Average wind velocity 
meters/second 


January 


5.0 


February 


6.6 


March 


4.3 


April 


4.4 


May 


5.6 


June 


5.4 


July 


4.5 


August 


3.6 


September 


4.1 


October 


4.4 


November 


5.9 


December 


6.7 


Average 


5.0 









(Ibarra and Davalos, 1991). 



312 



Table B-5 Estimates of monthly groundwater flow based on data and average monthly 
rainfall in the Yucatan. 



Month Share of annual rainfall, Groundwater flow, per 

Decimal square meter of mangrove wetland, 

m /m/yr 



January 


0.07 


604.1 






February 


0.04 


345.2 






March 


0.04 


345.2 






April 


0.04 


345.2 






May 


0.15 


1294.5 






June 
July 


0.13 
0.08 


1121.9 
690.4 






August 


0.09 


776.7 






September 


0.13 


1121.9 






October 


0.12 


103 5.6 






November 


0.06 


517.8 






December 


0.05 


431.5 






Total 


100 


8630 






Back (1985) 











313 



Table B-6 Net primary productivity (NPP) in mangrove ecosystems. 



Mangrove System 


NPP 
grams 


organic 


matter/m 2 /day 


NPP per yr 
(gOM/mVyr) 


Riverine 


12.6 






4600 




Basin 


5.6 






2044 




Fringe 


2.9 






1059 




Hummock 


2.6 






949 




Average 


5.85 






2163 




(Lugo and Brinson, 1979). 















































APPENDIX C 

COMPARISON WITH UNIVERSITY OF FLORIDA SEWAGE TREATMENT 

FACILITY 

Table D-l presents an emergy evaluation of the University of Florida Water 
Reclamation Facility. The University of Florida Water Reclamation Facility is an 
activated sludge wastewater plant similar to those used in many cities in the United 
States and Europe. It includes primary treatment with screens and grit chambers for 
removal of large particles, followed by alternating treatment in anaerobic and aerobic 
basins. Clarification, settling tanks allow sludge to settle and be removed. Effluent water 
is filtered and treated with chlorine for sterilization. Disposal is via groundwater injection 
(84%), use in air-conditioner cooling towers (8%) and use in campus irrigation (4%). 

Wastewater flow totals about 2 million gallons per day for a population of about 
40,000. This amounts to 50 gallons per person, however, since most of the population do 
not live on-campus, wastewater generation is even higher. If assumed to be equivalent to 
a full-time residence for 20,000 people, wastewater flow is around 100 gallons/person. 
Capital investment for the University of Florida treatment plant was around $1 1.2 million 

The University of Florida system is dependent on the use of much electricity 
(even ignoring electricity used to pump to the facility) and uses 4. 1 E6 kilowatt-hours 
annually to operate the mechanical aerators, grinders, and pumps. Chemicals are also 
used: alum for coagulation, chlorine for disinfection. Freshwater totaling 7.3 million 



314 



315 

gallons/year is used at the University of Florida facility for disinfection and general plant 
operations. 

Emergy analysis of the University of Florida treatment plant (Table 5-1) 
shows that >99% of resources are non-renewable (raw wastewater), and purchased goods 
are 0.5% and services 0.1%. Renewable resources contribute less than 0.001% of emergy 
inputs. The purchased / renewable ratio is 220 for the University of Florida facility (220 
times as much purchased inputs as renewable resource emergy inputs). Emergy required 
per person is 3 14 E14/person. Empower density (energy per area per time) is 14.3 E20 
sej/ha/yr. for the University of Florida system. 



316 



Table C-l Emergy analysis of the University of Florida sewage treatment facility. 



Note 


Item 


Data 


EMERGY/unit 
(sej/unit) 


SOLAR 

EMERGY 

(xE17sej) 


Em$* 


Renewable 












Resources 












1 


Sunlight 


2.6 E 13 J/yr 


1 


<0.001 


19 


2 


Wind 


2.53 E13 J/yr 


663 sej/J 


0.18 


12,244 



Subtotal 



0.18 



12,244 



Non-renewable 












resources 












3 
Purchased 


Raw sewage 


714.1 E6 
gallons/yr 


8.76 Ell 
sej/gallon 


6256 


456,644,230 


Goods 












4 
5 
6 
7 
8 
9 


Electricity 

Fuel 

Water 

Chlorine 

Capital Costs 

Maintenance 

(Goods) 


1.18 E13 J/yr 
1.52 Ell J/yr 

1.36 Ell J/yr 

6.37 El 1 J/yr 
$546,750 
$365,000 


173681 sej/J 
6.6 E4 sej/J 
665714 sej/J 
39800 sej/J 
1.37E12sej/$ 
1.37E12sej/$ 


20.49 

0.11 

0.91 

0.25 

7.49 

5.00 


1,825,552 

7,308 

66,085 

18,514 

546,750 

365,000 


Subtotal 
Purchased 








34.34 


2,829,209 


Goods 












10 
Services 


Operating and 
Maintenance 











Total 



1 1 Yield 



$385,118 1.37E12sej/$ 5.28 385,118 

6295.8 124,174,853 

Treated sewage 13.36 E13 4.71 E6 sej/J 6295.8 124,174,853 



♦Based on 1.37 EI2 sej/$, 1993 values (Odum, 1996, p. 3 14) 

Sunlight received in Gainesville, Florida with albedo estimated at 10% x .44 ha (size of sewage 
facility): (1.58 x 1 OE6 kcal/sq m/yr) (.90)(1 x 10 E4 sq m/ha) (4186 J/kcal) (0.44ha) 
= 2.62E 13 or 0.262E 14 J/yT (Odum, 1996, p. 1 14) 



Based on method given in Odum, 1996, p. 294, with values of eddy diffusion and 
vertical gradient from Tampa, Florida and using wind of 10 m height as relevant for re 



317 



Table C-l continued 

aeration of microbial reactor tanks of facility: (10 m)(I. 23 kg/cu m) (2. 8 cu m/m/sec) 
(3.154E7 sec/yr) (2.3 m/sec/m)E2 (4400 sq m) = 2.53 EI3 J/yr 
Transformity for wind from Odum, 1996 p. 186 

3 

Yearly inputs of raw sewage: 714.1 E6 gallons 

Transformity based on emergy needed to sustain people in Florida: 32 El 5 sej/yr (Odum et al, 
1998) 

divided by yearly outputs of wastewater per person = 100 gallons/day *365 days = 

(3.65E4 gallons) 

32 E15 sej/yr / 3.65 E4 gallons = 8.76 El 1 sej/gallon 

4 

Electricity chemical potential: (3,291,300)60 kWh/yr) (3.6E6 J/kWh) = 1. 1 8EI3 J/yr 
(Odum, 1996, p.300) 

Mean transformity for electricity (Odum, 1996, p. 305) 

5 

Fuel chemical potential based on P. Green, 1992, p. 27: (1000 gal/yr) (3.7 L/gal) (41E6 J/L) = 1. 
5 2E11 J/yr 

Fuel transformity based on calculation of Slesser, 1978 cited in Odum, 1996, p. '308 

6 

Water, Chemical Potential Energy: 

4940 J/kg given in Odum, 1996, p. 120, density of water at 20 deg C = 998.2 kg/ cu m (Kraut, 
Fluid Mechanics for Technicians, 1992, p. 365; (7,296,700 gal/yr) (I cu in/ 264 gal) (4940 J/kg) 
(998.2 kg/cu m) = 1.36EI I J/yr 

Transformity of water from Brown and Arding, 1991, Transformity Working Paper 

7 

Chlorine: (7E6 kcal/ton) (4186 J/kcal) (21.75 tons/yr) = 6.37EI 1 J/yr and the transformity of coal 
(Odum, 1996, p. 194) 

8 

Capital Costs: Facility excluding the sludge drying component 
$10,935,000/20 yrs lifetime = $546,750 x 1.37EI2 sej/$ = 749.05EI7 



318 
Table C-l continued 

9 

Maintenance (goods) $365,000 * 1.37 E12 sej/$ = 749.05 E17 

10 

Operation: labor costs: $385,1 18/yr x 1.37EI2 sej/$ = 527.61 E 17 sej 

11 

Discharge of treated wastewater: 714.1 E6 gallons/yr 

Chemical potential of wastewater: 714. 1E6 gal * 1 cu m/264 gal * 10E6 g/cu m * 4.94 J/g 

= 13.36E13J 

Transformity of treated wastewater: 6295.8 E17 sej / 13.36 E13 J = 4.71 E6 sej/J 












REFERENCES 

Actnicht, C, B. Friedheim and B. Conrad, 1995. Competition for electron donors among 
nitrate reducers, ferric iron reducers, sulfate reducers, and methanogens in anoxic paddy 
soils, Biol. Fertil. Soils, 19:65-72. 

APHA, 1995. Standard Methods for the Examination of Water and Wastewater, 19th 
Edition, American Public Health Association, Washington, D.C. 

Back, W., 1995. Water management by early people in the Yucatan, Mexico, 
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BIOGRAPHICAL SKETCH 

Mark Nelson was bom 29 May 1947, in Brooklyn, New York, and was educated 
at Dartmouth College, where he graduated Summa Cum Laude in 1968, with high honors 
in philosophy and was elected a member of Phi Beta Kappa. His M.S. degree (1995) is 
from the University of Arizona's School of Renewable Natural Resources, Tucson. 

A founding director and currently Chairman and C.E.O. of the Institute of 
Ecotechnics, London, Mark has worked in demonstration ecological projects in the 
United States and Australia for over two decades. His research interests includes pasture 
improvement and regeneration of tropical savannah ecology, high desert orchardry and 
silvicultural systems, ecological engineering and closed ecological systems. Mark served 
as director of Environmental and Space Applications for the Biosphere 2 project in 
Oracle, AZ from 1985-1994. He was a member of the eight-person biospherian crew that 
operated and researched Biosphere 2 during its first two year closure experiment, 1991- 
1993. He is currently a Contributing Editor for the journal, Life Support and Biosphere 
Science. 

As Vice President for Wastewater Recycling Systems for Planetary Coral Reef 
Foundation, he has designed and implemented constructed wetland systems in Mexico, 
Bali and the United States. He is also a director of Eco-Frontiers, Inc., which owns and 
manages projects in a number of challenging environments around the world. 

330 



I certify that I have read this study and that in my opinion it conforms to 
acceptable standards of scholarly presentation and is fully adequate, in scope and quality, 
as a dissertation for the degree of Doctor of Philosophy. 

Howard T. Odum, Chairman 
Graduate Research Professor 
of Environmental Engineering Sciences 

I certify that I have read this study and that in my opinion it conforms to 
acceptable standards of scholarly presentation and is fully adequate, in scope and quality, 
as a dissertation for the degree of Doctor of Philosophy. 




Mark T. Brown, Co-chairman 
Assistant Professor 
of Environmental Engineering Sciences 

I certify that I have read this study and that in my opinion it conforms to 
acceptable standards of scholarly presentation and is fully adequate, in scope and quality, 
as a dissertation for the degree of Doctor of Philosophy. 




/77?^5r> 



Clay IV Montague / 
Associate Professor 
of Environmental Engineering Sciences 



I certify that I have read this study and that in my opinion it conforms to 
acceptable standards of scholarly presentation and is fully adequate, in scope and quality, 
as a dissertation for the degree of Doctor of Philosopt 




Konda R. Reddy 
Graduate Research Professor 
of Soil and Water Science 

I certify that I have read this study and that in my opinion it conforms to 
acceptable standards of scholarly presentation and is fully adequate, in scope and quality, 
as a dissertation for the degree of Doctor ofJEhriesophy. 




Daniel P. Spangler 
Associate Professor of Geology 
This dissertation was submitted to the Graduate Faculty of the College of 
Engineering and to the Graduate School and was accepted as partial fulfillment of the 
requirements for the degree of Doctor of Philosophy. 






December 1998 



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Winfred M. Phillips 

Dean, College of Engineering 



M.J. Ohanian 

Dean, Graduate School 
























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